Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /var/tmp/portage/net-libs/libtorrent-rasterbar-2.0.3/work/libtorrent-rasterbar-2.0.3_build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/ninja cmTC_bb004 && [1/2] Building C object CMakeFiles/cmTC_bb004.dir/src.c.o
[2/2] Linking C executable cmTC_bb004
FAILED: cmTC_bb004 
: && /usr/bin/x86_64-pc-linux-gnu-gcc -march=native -pipe -O2 -fomit-frame-pointer -Wl,-O2 -Wl,--as-needed -Wl,--sort-common -Wl,--hash-style=gnu CMakeFiles/cmTC_bb004.dir/src.c.o -o cmTC_bb004   && :
/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: CMakeFiles/cmTC_bb004.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/11.1.0/../../../../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/11.1.0/../../../../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/11.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: src.c:(.text.startup+0x40): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.


Source file was:
#include <pthread.h>

static 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/libtorrent-rasterbar-2.0.3/work/libtorrent-rasterbar-2.0.3_build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/ninja cmTC_d9754 && [1/2] Building C object CMakeFiles/cmTC_d9754.dir/CheckFunctionExists.c.o
[2/2] Linking C executable cmTC_d9754
FAILED: cmTC_d9754 
: && /usr/bin/x86_64-pc-linux-gnu-gcc -march=native -pipe -O2 -fomit-frame-pointer -DCHECK_FUNCTION_EXISTS=pthread_create -Wl,-O2 -Wl,--as-needed -Wl,--sort-common -Wl,--hash-style=gnu CMakeFiles/cmTC_d9754.dir/CheckFunctionExists.c.o -o cmTC_d9754  -lpthreads && :
/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.