When trying to build egl driver under ArchLinux, there is erros while linking:

-------8<-------
make[3]: Leaving directory `/build/src/mesa-b033f050fd5179b051181a0a4b6d94110624d25c/src/gallium/winsys/nouveau/drm'
make[2]: Leaving directory `/build/src/mesa-b033f050fd5179b051181a0a4b6d94110624d25c/src/gallium/winsys'
make[2]: Entering directory `/build/src/mesa-b033f050fd5179b051181a0a4b6d94110624d25c/src/gallium/targets'
make[3]: Entering directory `/build/src/mesa-b033f050fd5179b051181a0a4b6d94110624d25c/src/gallium/targets/egl-static'
gcc -c -o egl.o egl.c -DFEATURE_ES1=1 -DFEATURE_ES2=1 -DFEATURE_GL=1 -DGALLIUM_RBUG -DGALLIUM_SOFTPIPE -DGALLIUM_TRACE -D_EGL_EXTERNAL_GL=1 -D_EGL_MAIN=_eglMain -D_EGL_PIPE_NOUVEAU=1 -D_EGL_PIPE_R300=1 -D_EGL_PIPE_R600=1 -I../../../../include -I../../../../src/egl/main -I../../../../src/gallium/auxiliary -I../../../../src/gallium/drivers -I../../../../src/gallium/include -I../../../../src/gallium/state_trackers/egl -I../../../../src/gallium/winsys -I../../../../src/mesa -I/usr/include/libdrm -DGALLIUM_LLVMPIPE -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -march=x86-64 -mtune=generic -O2 -pipe -Wall -Wmissing-prototypes -std=c99 -ffast-math -fno-strict-aliasing -fPIC -DUSE_X86_64_ASM -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -fvisibility=hidden
gcc -c -o egl_pipe.o egl_pipe.c -DFEATURE_ES1=1 -DFEATURE_ES2=1 -DFEATURE_GL=1 -DGALLIUM_RBUG -DGALLIUM_SOFTPIPE -DGALLIUM_TRACE -D_EGL_EXTERNAL_GL=1 -D_EGL_MAIN=_eglMain -D_EGL_PIPE_NOUVEAU=1 -D_EGL_PIPE_R300=1 -D_EGL_PIPE_R600=1 -I../../../../include -I../../../../src/egl/main -I../../../../src/gallium/auxiliary -I../../../../src/gallium/drivers -I../../../../src/gallium/include -I../../../../src/gallium/state_trackers/egl -I../../../../src/gallium/winsys -I../../../../src/mesa -I/usr/include/libdrm -DGALLIUM_LLVMPIPE -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -march=x86-64 -mtune=generic -O2 -pipe -Wall -Wmissing-prototypes -std=c99 -ffast-math -fno-strict-aliasing -fPIC -DUSE_X86_64_ASM -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -fvisibility=hidden
gcc -c -o egl_st.o egl_st.c -DFEATURE_ES1=1 -DFEATURE_ES2=1 -DFEATURE_GL=1 -DGALLIUM_RBUG -DGALLIUM_SOFTPIPE -DGALLIUM_TRACE -D_EGL_EXTERNAL_GL=1 -D_EGL_MAIN=_eglMain -D_EGL_PIPE_NOUVEAU=1 -D_EGL_PIPE_R300=1 -D_EGL_PIPE_R600=1 -I../../../../include -I../../../../src/egl/main -I../../../../src/gallium/auxiliary -I../../../../src/gallium/drivers -I../../../../src/gallium/include -I../../../../src/gallium/state_trackers/egl -I../../../../src/gallium/winsys -I../../../../src/mesa -I/usr/include/libdrm -DGALLIUM_LLVMPIPE -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -march=x86-64 -mtune=generic -O2 -pipe -Wall -Wmissing-prototypes -std=c99 -ffast-math -fno-strict-aliasing -fPIC -DUSE_X86_64_ASM -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -fvisibility=hidden
gcc -c -o st_GL.o st_GL.c -I ../../../../src/mesa -I../../../../src/gallium/include -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -march=x86-64 -mtune=generic -O2 -pipe -Wall -Wmissing-prototypes -std=c99 -ffast-math -fno-strict-aliasing -fPIC -DUSE_X86_64_ASM -D_GNU_SOURCE -DPTHREADS -DTEXTURE_FLOAT_ENABLED -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DGLX_USE_TLS -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DGLX_DIRECT_RENDERING -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS -DHAVE_LIBUDEV -DHAVE_XCB_DRI2 -DXCB_DRI2_CONNECT_DEVICE_NAME_BROKEN -DGALLIUM_LLVMPIPE -D__STDC_CONSTANT_MACROS -DHAVE_LLVM=0x0209 -fvisibility=hidden
egl_st.c: In function 'dlopen_gl_lib_cb':
egl_st.c:58:13: warning: field precision specifier '.*' expects argument of type 'int', but argument 4 has type 'size_t' [-Wformat]
egl_st.c:58:13: warning: field precision specifier '.*' expects argument of type 'int', but argument 4 has type 'size_t' [-Wformat]
/bin/sh ../../../../bin/mklib -o st_GL.so -noprefix -linker 'g++' \
-ldflags '-L../../../../lib -Wl,--hash-style=gnu -Wl,--as-needed -L/usr/lib/llvm -lpthread -lffi -ldl -lm ' \
-cplusplus -install ../../../../lib/egl \
st_GL.o -Wl,--start-group ../../../../src/mesa/libmesagallium.a ../../../../src/gallium/auxiliary/libgallium.a -Wl,--end-group \
-lm -lpthread -ldl -lLLVMObject -lLLVMMCJIT -lLLVMMCDisassembler -lLLVMXCoreCodeGen -lLLVMXCoreInfo -lLLVMSystemZCodeGen -lLLVMSystemZInfo -lLLVMSparcCodeGen -lLLVMSparcInfo -lLLVMPowerPCCodeGen -lLLVMPowerPCInfo -lLLVMPowerPCAsmPrinter -lLLVMPTXCodeGen -lLLVMPTXInfo -lLLVMMipsCodeGen -lLLVMMipsInfo -lLLVMMSP430CodeGen -lLLVMMSP430Info -lLLVMMSP430AsmPrinter -lLLVMMBlazeDisassembler -lLLVMMBlazeAsmParser -lLLVMMBlazeCodeGen -lLLVMMBlazeAsmPrinter -lLLVMMBlazeInfo -lLLVMLinker -lLLVMipo -lLLVMInterpreter -lLLVMInstrumentation -lLLVMJIT -lLLVMExecutionEngine -lLLVMCppBackend -lLLVMCppBackendInfo -lLLVMCellSPUCodeGen -lLLVMCellSPUInfo -lLLVMCBackend -lLLVMCBackendInfo -lLLVMBlackfinCodeGen -lLLVMBlackfinInfo -lLLVMBitWriter -lLLVMX86Disassembler -lLLVMX86AsmParser -lLLVMX86CodeGen -lLLVMX86AsmPrinter -lLLVMX86Utils -lLLVMX86Info -lLLVMAsmParser -lLLVMARMDisassembler -lLLVMARMAsmParser -lLLVMARMCodeGen -lLLVMARMAsmPrinter -lLLVMARMInfo -lLLVMArchive -lLLVMBitReader -lLLVMAlphaCodeGen -lLLVMSelectionDAG -lLLVMAsmPrinter -lLLVMMCParser -lLLVMCodeGen -lLLVMScalarOpts -lLLVMInstCombine -lLLVMTransformUtils -lLLVMipa -lLLVMAnalysis -lLLVMTarget -lLLVMCore -lLLVMAlphaInfo -lLLVMMC -lLLVMSupport -lstdc++
mklib: Making Linux shared library: st_GL.so
/bin/sh ../../../../bin/mklib -o egl_gallium.so -noprefix -linker 'g++' \
-ldflags '-L../../../../lib -Wl,--no-undefined -Wl,--hash-style=gnu -Wl,--as-needed -L/usr/lib/llvm -lpthread -lffi -ldl -lm ' \
-cplusplus -install ../../../../lib/egl \
egl.o egl_pipe.o egl_st.o -Wl,--start-group ../../../../src/gallium/auxiliary/libgallium.a ../../../../src/gallium/drivers/identity/libidentity.a ../../../../src/gallium/drivers/nouveau/libnouveau.a ../../../../src/gallium/drivers/nv50/libnv50.a ../../../../src/gallium/drivers/nvc0/libnvc0.a ../../../../src/gallium/drivers/nvfx/libnvfx.a ../../../../src/gallium/drivers/r300/libr300.a ../../../../src/gallium/drivers/r600/libr600.a ../../../../src/gallium/drivers/rbug/librbug.a ../../../../src/gallium/drivers/softpipe/libsoftpipe.a ../../../../src/gallium/drivers/trace/libtrace.a ../../../../src/gallium/state_trackers/egl/libegl.a ../../../../src/gallium/winsys/nouveau/drm/libnouveaudrm.a ../../../../src/gallium/winsys/r600/drm/libr600winsys.a ../../../../src/gallium/winsys/radeon/drm/libradeonwinsys.a ../../../../src/gallium/winsys/sw/xlib/libws_xlib.a ../../../../src/gallium/drivers/llvmpipe/libllvmpipe.a -Wl,--end-group \
-lEGL -lX11 -lXext -lXfixes -ldl -ldrm -ldrm_nouveau -ldrm_radeon -lm -lrt -ludev -lLLVMObject -lLLVMMCJIT -lLLVMMCDisassembler -lLLVMXCoreCodeGen -lLLVMXCoreInfo -lLLVMSystemZCodeGen -lLLVMSystemZInfo -lLLVMSparcCodeGen -lLLVMSparcInfo -lLLVMPowerPCCodeGen -lLLVMPowerPCInfo -lLLVMPowerPCAsmPrinter -lLLVMPTXCodeGen -lLLVMPTXInfo -lLLVMMipsCodeGen -lLLVMMipsInfo -lLLVMMSP430CodeGen -lLLVMMSP430Info -lLLVMMSP430AsmPrinter -lLLVMMBlazeDisassembler -lLLVMMBlazeAsmParser -lLLVMMBlazeCodeGen -lLLVMMBlazeAsmPrinter -lLLVMMBlazeInfo -lLLVMLinker -lLLVMipo -lLLVMInterpreter -lLLVMInstrumentation -lLLVMJIT -lLLVMExecutionEngine -lLLVMCppBackend -lLLVMCppBackendInfo -lLLVMCellSPUCodeGen -lLLVMCellSPUInfo -lLLVMCBackend -lLLVMCBackendInfo -lLLVMBlackfinCodeGen -lLLVMBlackfinInfo -lLLVMBitWriter -lLLVMX86Disassembler -lLLVMX86AsmParser -lLLVMX86CodeGen -lLLVMX86AsmPrinter -lLLVMX86Utils -lLLVMX86Info -lLLVMAsmParser -lLLVMARMDisassembler -lLLVMARMAsmParser -lLLVMARMCodeGen -lLLVMARMAsmPrinter -lLLVMARMInfo -lLLVMArchive -lLLVMBitReader -lLLVMAlphaCodeGen -lLLVMSelectionDAG -lLLVMAsmPrinter -lLLVMMCParser -lLLVMCodeGen -lLLVMScalarOpts -lLLVMInstCombine -lLLVMTransformUtils -lLLVMipa -lLLVMAnalysis -lLLVMTarget -lLLVMCore -lLLVMAlphaInfo -lLLVMMC -lLLVMSupport -lstdc++
mklib: Making Linux shared library: egl_gallium.so
../../../../src/gallium/drivers/rbug/librbug.a(rbug_core.o): In function `pipe_thread_create.constprop.17':
rbug_core.c:(.text+0x13c9): undefined reference to `pthread_sigmask'
rbug_core.c:(.text+0x13e2): undefined reference to `pthread_create'
rbug_core.c:(.text+0x13f3): undefined reference to `pthread_sigmask'
../../../../src/gallium/drivers/rbug/librbug.a(rbug_core.o): In function `rbug_stop':
rbug_core.c:(.text+0x1474): undefined reference to `pthread_join'
../../../../src/gallium/winsys/radeon/drm/libradeonwinsys.a(radeon_drm_cs.o): In function `pipe_thread_create.constprop.7':
radeon_drm_cs.c:(.text+0x2b9): undefined reference to `pthread_sigmask'
radeon_drm_cs.c:(.text+0x2d2): undefined reference to `pthread_create'
radeon_drm_cs.c:(.text+0x2e3): undefined reference to `pthread_sigmask'
../../../../src/gallium/winsys/radeon/drm/libradeonwinsys.a(radeon_drm_cs.o): In function `radeon_drm_cs_sync_flush':
radeon_drm_cs.c:(.text+0x95b): undefined reference to `pthread_join'
../../../../src/gallium/drivers/llvmpipe/libllvmpipe.a(lp_rast.o): In function `pipe_thread_create.constprop.5':
lp_rast.c:(.text+0x539): undefined reference to `pthread_sigmask'
lp_rast.c:(.text+0x552): undefined reference to `pthread_create'
lp_rast.c:(.text+0x563): undefined reference to `pthread_sigmask'
../../../../src/gallium/drivers/llvmpipe/libllvmpipe.a(lp_rast.o): In function `thread_func':
lp_rast.c:(.text+0x615): undefined reference to `pthread_barrier_wait'
lp_rast.c:(.text+0x629): undefined reference to `pthread_barrier_wait'
../../../../src/gallium/drivers/llvmpipe/libllvmpipe.a(lp_rast.o): In function `lp_rast_create':
lp_rast.c:(.text+0xf2b): undefined reference to `pthread_barrier_init'
../../../../src/gallium/drivers/llvmpipe/libllvmpipe.a(lp_rast.o): In function `lp_rast_destroy':
lp_rast.c:(.text+0xffa): undefined reference to `pthread_join'
lp_rast.c:(.text+0x1064): undefined reference to `pthread_barrier_destroy'
/usr/lib/llvm/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x31): undefined reference to `pthread_mutexattr_init'
/usr/lib/llvm/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x3d): undefined reference to `pthread_mutexattr_settype'
/usr/lib/llvm/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x47): undefined reference to `pthread_mutexattr_setpshared'
/usr/lib/llvm/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::MutexImpl(bool)':
(.text+0x5a): undefined reference to `pthread_mutexattr_destroy'
/usr/lib/llvm/libLLVMSupport.a(Mutex.o): In function `llvm::sys::MutexImpl::tryacquire()':
(.text+0xe8): undefined reference to `pthread_mutex_trylock'
/usr/lib/llvm/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::RWMutexImpl()':
(.text+0x2b): undefined reference to `pthread_rwlock_init'
/usr/lib/llvm/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::~RWMutexImpl()':
(.text+0x58): undefined reference to `pthread_rwlock_destroy'
/usr/lib/llvm/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::reader_acquire()':
(.text+0x78): undefined reference to `pthread_rwlock_rdlock'
/usr/lib/llvm/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::reader_release()':
(.text+0x98): undefined reference to `pthread_rwlock_unlock'
/usr/lib/llvm/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::writer_acquire()':
(.text+0xb8): undefined reference to `pthread_rwlock_wrlock'
/usr/lib/llvm/libLLVMSupport.a(RWMutex.o): In function `llvm::sys::RWMutexImpl::writer_release()':
(.text+0xd8): undefined reference to `pthread_rwlock_unlock'
/usr/lib/llvm/libLLVMSupport.a(ThreadLocal.o): In function `llvm::sys::ThreadLocalImpl::~ThreadLocalImpl()':
(.text+0x16): undefined reference to `pthread_key_delete'
/usr/lib/llvm/libLLVMSupport.a(ThreadLocal.o): In function `llvm::sys::ThreadLocalImpl::ThreadLocalImpl()':
(.text+0x8a): undefined reference to `pthread_key_create'
/usr/lib/llvm/libLLVMSupport.a(ThreadLocal.o): In function `llvm::sys::ThreadLocalImpl::setInstance(void const*)':
(.text+0xb7): undefined reference to `pthread_setspecific'
/usr/lib/llvm/libLLVMSupport.a(ThreadLocal.o): In function `llvm::sys::ThreadLocalImpl::getInstance()':
(.text+0xc7): undefined reference to `pthread_getspecific'
/usr/lib/llvm/libLLVMSupport.a(Threading.o): In function `llvm::llvm_execute_on_thread(void (*)(void*), void*, unsigned int)':
(.text+0x126): undefined reference to `pthread_create'
/usr/lib/llvm/libLLVMSupport.a(Threading.o): In function `llvm::llvm_execute_on_thread(void (*)(void*), void*, unsigned int)':
(.text+0x146): undefined reference to `pthread_attr_setstacksize'
/usr/lib/llvm/libLLVMSupport.a(Threading.o): In function `llvm::llvm_execute_on_thread(void (*)(void*), void*, unsigned int)':
(.text+0x158): undefined reference to `pthread_join'
collect2: ld returned 1 exit status
mklib: Installing egl_gallium.so in ../../../../lib/egl
mklib: Installing st_GL.so in ../../../../lib/egl
mv: cannot stat `egl_gallium.so': No such file or directory
make[3]: Leaving directory `/build/src/mesa-b033f050fd5179b051181a0a4b6d94110624d25c/src/gallium/targets/egl-static'
------->8-------

A workaround to get it building is to filter -Wl,--as-needed from LDFLAGS. This problem seems present since the comming of egl-static target.

See https://bugs.archlinux.org/task/25093