Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_24679/fast && gmake[3]: Entering directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'
/usr/bin/gmake  -f CMakeFiles/cmTC_24679.dir/build.make CMakeFiles/cmTC_24679.dir/build
gmake[4]: Entering directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_24679.dir/src.c.o
/usr/lib/llvm/10/bin/x86_64-pc-linux-gnu-clang   -O2 -pipe -march=native -frecord-gcc-switches -fno-diagnostics-color -DCMAKE_HAVE_LIBC_PTHREAD -o CMakeFiles/cmTC_24679.dir/src.c.o -c /var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_24679
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_24679.dir/link.txt --verbose=1
/usr/lib/llvm/10/bin/x86_64-pc-linux-gnu-clang -O2 -pipe -march=native -frecord-gcc-switches -fno-diagnostics-color -DCMAKE_HAVE_LIBC_PTHREAD -Wl,-O1 -Wl,--as-needed -Wl,--defsym=__gentoo_check_ldflags__=0 -fuse-ld=lld  CMakeFiles/cmTC_24679.dir/src.c.o -o cmTC_24679 
ld.lld: error: undefined symbol: pthread_create
>>> referenced by src.c
>>>               CMakeFiles/cmTC_24679.dir/src.c.o:(main)

ld.lld: error: undefined symbol: pthread_detach
>>> referenced by src.c
>>>               CMakeFiles/cmTC_24679.dir/src.c.o:(main)

ld.lld: error: undefined symbol: pthread_cancel
>>> referenced by src.c
>>>               CMakeFiles/cmTC_24679.dir/src.c.o:(main)

ld.lld: error: undefined symbol: pthread_join
>>> referenced by src.c
>>>               CMakeFiles/cmTC_24679.dir/src.c.o:(main)
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
gmake[4]: *** [CMakeFiles/cmTC_24679.dir/build.make:106: cmTC_24679] Error 1
gmake[4]: Leaving directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'
gmake[3]: *** [Makefile:140: cmTC_24679/fast] Error 2
gmake[3]: Leaving directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'


Source file was:
#include <pthread.h>

void* test_func(void* data)
{
  return data;
}

int main(void)
{
  pthread_t thread;
  pthread_create(&thread, NULL, test_func, NULL);
  pthread_detach(thread);
  pthread_cancel(thread);
  pthread_join(thread, NULL);
  pthread_atfork(NULL, NULL, NULL);
  pthread_exit(NULL);

  return 0;
}

Determining if the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_ec3db/fast && gmake[3]: Entering directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'
/usr/bin/gmake  -f CMakeFiles/cmTC_ec3db.dir/build.make CMakeFiles/cmTC_ec3db.dir/build
gmake[4]: Entering directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_ec3db.dir/CheckFunctionExists.c.o
/usr/lib/llvm/10/bin/x86_64-pc-linux-gnu-clang   -O2 -pipe -march=native -frecord-gcc-switches -fno-diagnostics-color -DCHECK_FUNCTION_EXISTS=pthread_create -o CMakeFiles/cmTC_ec3db.dir/CheckFunctionExists.c.o -c /usr/share/cmake/Modules/CheckFunctionExists.c
Linking C executable cmTC_ec3db
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_ec3db.dir/link.txt --verbose=1
/usr/lib/llvm/10/bin/x86_64-pc-linux-gnu-clang -O2 -pipe -march=native -frecord-gcc-switches -fno-diagnostics-color -DCHECK_FUNCTION_EXISTS=pthread_create -Wl,-O1 -Wl,--as-needed -Wl,--defsym=__gentoo_check_ldflags__=0 -fuse-ld=lld  CMakeFiles/cmTC_ec3db.dir/CheckFunctionExists.c.o -o cmTC_ec3db  -lpthreads 
ld.lld: error: unable to find library -lpthreads
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
gmake[4]: *** [CMakeFiles/cmTC_ec3db.dir/build.make:106: cmTC_ec3db] Error 1
gmake[4]: Leaving directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'
gmake[3]: *** [Makefile:140: cmTC_ec3db/fast] Error 2
gmake[3]: Leaving directory '/var/tmp/portage/net-libs/google-cloud-cpp-0.10.0-r1/work/google-cloud-cpp-0.10.0_build/external/googleapis/src/googleapis_project-build/CMakeFiles/CMakeTmp'