Created attachment 133754 [details]
build.log

WIth the source tarball from https://dri.freedesktop.org/libdrm/${P}.tar.bz2, I get, on a Gentoo system:

(...)
Making all in radeon
libtool: link: x86_64-pc-linux-gnu-gcc -Wall -Wextra -Wsign-compare -Werror-implicit-function-declaration -Wpointer-arith -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -Wnested-externs -Wpacked -Wswitch-enum -Wmissing-format-attribute -Wstrict-aliasing=2 -Winit-self -Wdeclaration-after-statement -Wold-style-definition -Wno-unused-parameter -Wno-attributes -Wno-long-long -Winline -Wshadow -Wno-missing-field-initializers -I /var/tmp/portage/x11-libs/libdrm-2.4.83/work/libdrm-2.4.83/include/drm -I /var/tmp/portage/x11-libs/libdrm-2.4.83/work/libdrm-2.4.83 -O2 -march=native -pipe -fomit-frame-pointer -Wl,-O1 -o .libs/radeon_ttm rbo.o radeon_ttm.o  -Wl,--as-needed ../../.libs/libdrm.so -lm
Making all in amdgpu
/var/tmp/portage/x11-libs/libdrm-2.4.83/work/libdrm-2.4.83/tests/amdgpu/basic_tests.c: In function ‘amdgpu_userptr_test’:
/var/tmp/portage/x11-libs/libdrm-2.4.83/work/libdrm-2.4.83/tests/amdgpu/basic_tests.c:1369:2: warning: ignoring return value of ‘posix_memalign’, declared with attribute warn_unused_result [-Wunused-result]
  posix_memalign(&ptr, sysconf(_SC_PAGE_SIZE), BUFFER_SIZE);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/x11-libs/libdrm-2.4.83/work/libdrm-2.4.83/tests/amdgpu/uvd_enc_tests.c:39:20: fatal error: uve_ib.h: No such file or directory
 #include "uve_ib.h"
                    ^
compilation terminated.
make[3]: *** [amdgpu_test-uvd_enc_tests.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [all-recursive] Error 1
make[1]: *** [all-recursive] Error 1

Full build log in attachment