Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /var/tmp/portage/net-wireless/suscan-0.1.0/work/suscan-0.1.0_build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_1d783/fast && /usr/bin/gmake  -f CMakeFiles/cmTC_1d783.dir/build.make CMakeFiles/cmTC_1d783.dir/build
gmake[1]: Entering directory '/var/tmp/portage/net-wireless/suscan-0.1.0/work/suscan-0.1.0_build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_1d783.dir/src.c.o
/usr/bin/x86_64-pc-linux-gnu-gcc    -O2 -pipe -march=native -frecord-gcc-switches -DCMAKE_HAVE_LIBC_PTHREAD -o CMakeFiles/cmTC_1d783.dir/src.c.o -c /var/tmp/portage/net-wireless/suscan-0.1.0/work/suscan-0.1.0_build/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_1d783
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_1d783.dir/link.txt --verbose=1
/usr/bin/x86_64-pc-linux-gnu-gcc -O2 -pipe -march=native -frecord-gcc-switches -DCMAKE_HAVE_LIBC_PTHREAD -Wl,-O1 -Wl,--as-needed -Wl,--defsym=__gentoo_check_ldflags__=0  CMakeFiles/cmTC_1d783.dir/src.c.o -o cmTC_1d783 
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/cmTC_1d783.dir/src.c.o: in function `main':
src.c:(.text.startup+0x23): undefined reference to `pthread_create'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: src.c:(.text.startup+0x2c): undefined reference to `pthread_detach'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: src.c:(.text.startup+0x35): undefined reference to `pthread_cancel'
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: src.c:(.text.startup+0x40): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
gmake[1]: *** [CMakeFiles/cmTC_1d783.dir/build.make:106: cmTC_1d783] Error 1
gmake[1]: Leaving directory '/var/tmp/portage/net-wireless/suscan-0.1.0/work/suscan-0.1.0_build/CMakeFiles/CMakeTmp'
gmake: *** [Makefile:140: cmTC_1d783/fast] Error 2


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-wireless/suscan-0.1.0/work/suscan-0.1.0_build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_81637/fast && /usr/bin/gmake  -f CMakeFiles/cmTC_81637.dir/build.make CMakeFiles/cmTC_81637.dir/build
gmake[1]: Entering directory '/var/tmp/portage/net-wireless/suscan-0.1.0/work/suscan-0.1.0_build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_81637.dir/CheckFunctionExists.c.o
/usr/bin/x86_64-pc-linux-gnu-gcc    -O2 -pipe -march=native -frecord-gcc-switches -DCHECK_FUNCTION_EXISTS=pthread_create -o CMakeFiles/cmTC_81637.dir/CheckFunctionExists.c.o -c /usr/share/cmake/Modules/CheckFunctionExists.c
Linking C executable cmTC_81637
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_81637.dir/link.txt --verbose=1
/usr/bin/x86_64-pc-linux-gnu-gcc -O2 -pipe -march=native -frecord-gcc-switches -DCHECK_FUNCTION_EXISTS=pthread_create -Wl,-O1 -Wl,--as-needed -Wl,--defsym=__gentoo_check_ldflags__=0  CMakeFiles/cmTC_81637.dir/CheckFunctionExists.c.o -o cmTC_81637  -lpthreads 
/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
gmake[1]: *** [CMakeFiles/cmTC_81637.dir/build.make:106: cmTC_81637] Error 1
gmake[1]: Leaving directory '/var/tmp/portage/net-wireless/suscan-0.1.0/work/suscan-0.1.0_build/CMakeFiles/CMakeTmp'
gmake: *** [Makefile:140: cmTC_81637/fast] Error 2