Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /var/tmp/portage/games-arcade/commandergenius-2.4.0/work/commandergenius-2.4.0_build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/ninja cmTC_d66d6 && [1/2] Building C object CMakeFiles/cmTC_d66d6.dir/src.c.o
[2/2] Linking C executable cmTC_d66d6
FAILED: cmTC_d66d6 
: && /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_d66d6.dir/src.c.o -o cmTC_d66d6   && :
ld.lld: error: undefined symbol: pthread_create
>>> referenced by src.c
>>>               CMakeFiles/cmTC_d66d6.dir/src.c.o:(main)

ld.lld: error: undefined symbol: pthread_detach
>>> referenced by src.c
>>>               CMakeFiles/cmTC_d66d6.dir/src.c.o:(main)

ld.lld: error: undefined symbol: pthread_cancel
>>> referenced by src.c
>>>               CMakeFiles/cmTC_d66d6.dir/src.c.o:(main)

ld.lld: error: undefined symbol: pthread_join
>>> referenced by src.c
>>>               CMakeFiles/cmTC_d66d6.dir/src.c.o:(main)
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.


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/games-arcade/commandergenius-2.4.0/work/commandergenius-2.4.0_build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/ninja cmTC_f1a1e && [1/2] Building C object CMakeFiles/cmTC_f1a1e.dir/CheckFunctionExists.c.o
[2/2] Linking C executable cmTC_f1a1e
FAILED: cmTC_f1a1e 
: && /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_f1a1e.dir/CheckFunctionExists.c.o -o cmTC_f1a1e  -lpthreads && :
ld.lld: error: unable to find library -lpthreads
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.