Determining if the pthread_create exist failed with the following output:
Change Dir: /home/emile/DSIK_C/cmake-build-debug/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_ea9db/fast"
/usr/bin/make -f CMakeFiles/cmTC_ea9db.dir/build.make CMakeFiles/cmTC_ea9db.dir/build
make[1]: Entering directory '/home/emile/DSIK_C/cmake-build-debug/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_ea9db.dir/CheckSymbolExists.c.o
/usr/bin/cc   -std=gnu11 -o CMakeFiles/cmTC_ea9db.dir/CheckSymbolExists.c.o   -c /home/emile/DSIK_C/cmake-build-debug/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_ea9db
/home/emile/Downloads/clion-2018.3.3/bin/cmake/linux/bin/cmake -E cmake_link_script CMakeFiles/cmTC_ea9db.dir/link.txt --verbose=1
/usr/bin/cc      CMakeFiles/cmTC_ea9db.dir/CheckSymbolExists.c.o  -o cmTC_ea9db 
/usr/bin/ld: CMakeFiles/cmTC_ea9db.dir/CheckSymbolExists.c.o: in function `main':
CheckSymbolExists.c:(.text+0x1b): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
make[1]: *** [CMakeFiles/cmTC_ea9db.dir/build.make:87: cmTC_ea9db] Error 1
make[1]: Leaving directory '/home/emile/DSIK_C/cmake-build-debug/CMakeFiles/CMakeTmp'
make: *** [Makefile:121: cmTC_ea9db/fast] Error 2

File /home/emile/DSIK_C/cmake-build-debug/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <pthread.h>

int main(int argc, char** argv)
{
  (void)argv;
#ifndef pthread_create
  return ((int*)(&pthread_create))[argc];
#else
  (void)argc;
  return 0;
#endif
}