In Mesa-7.10.0, src/mesa/Makefile contains

osmesa_pcedit = sed \
        $(pcedit) \
        -e 's,@OSMESA_LIB@,$(OSMESA_LIB),' \
        -e 's,@OSMESA_PC_REQ@,$(OSMESA_PC_REQ),' \
        -e 's,@OSMESA_PC_LIB_PRIV@,$(OSMESA_PC_LIB_PRIV),'

In my case:

OSMESA_PC_LIB_PRIV is expanded to -lm -lpthread  -ldl -Wl,-rpath,/usr/lib64 -L/usr/lib64 -ltalloc

which leads to the sed expression:

sed ... -e 's,@OSMESA_PC_LIB_PRIV@,-lm -lpthread  -ldl -Wl,-rpath,/usr/lib64 -L/usr/lib64 -ltalloc  ,' osmesa.pc.in > osmesa.pc

This sed expression has unforeseen commas and is therefore invalid.

I suggest replacing the comma in the Makefile with some other symbol, e.g. %

The same applies for the generation of src/mesa/gl.pc,  which produces -e 's,@GL_PC_LIB_PRIV@,-lm -lpthread -Wl,-rpath,/usr/lib64 -L/usr/lib64 -ltalloc  ,'.

The same applies for the generation of ./src/egl/main/egl.pc .