Determining if the pthread_create exist failed with the following output:
Change Dir: /home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_b83fe/fast"
make[2]: Entering directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_b83fe.dir/build.make CMakeFiles/cmTC_b83fe.dir/build
make[3]: Entering directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_b83fe.dir/CheckSymbolExists.c.o
/usr/bin/cc    -o CMakeFiles/cmTC_b83fe.dir/CheckSymbolExists.c.o   -c /home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_b83fe
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_b83fe.dir/link.txt --verbose=1
/usr/bin/cc      -rdynamic CMakeFiles/cmTC_b83fe.dir/CheckSymbolExists.c.o  -o cmTC_b83fe 
CMakeFiles/cmTC_b83fe.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text+0x1b): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
make[3]: *** [CMakeFiles/cmTC_b83fe.dir/build.make:87: cmTC_b83fe] Error 1
make[3]: Leaving directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'
make[2]: *** [Makefile:126: cmTC_b83fe/fast] Error 2
make[2]: Leaving directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'

File /home/linus/ws/breakhack/build/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
}

Determining if the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_6c009/fast"
make[2]: Entering directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_6c009.dir/build.make CMakeFiles/cmTC_6c009.dir/build
make[3]: Entering directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_6c009.dir/CheckFunctionExists.c.o
/usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create   -o CMakeFiles/cmTC_6c009.dir/CheckFunctionExists.c.o   -c /usr/share/cmake-3.11/Modules/CheckFunctionExists.c
Linking C executable cmTC_6c009
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_6c009.dir/link.txt --verbose=1
/usr/bin/cc  -DCHECK_FUNCTION_EXISTS=pthread_create    -rdynamic CMakeFiles/cmTC_6c009.dir/CheckFunctionExists.c.o  -o cmTC_6c009 -lpthreads 
/usr/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[3]: *** [CMakeFiles/cmTC_6c009.dir/build.make:87: cmTC_6c009] Error 1
make[3]: Leaving directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'
make[2]: *** [Makefile:126: cmTC_6c009/fast] Error 2
make[2]: Leaving directory '/home/linus/ws/breakhack/build/CMakeFiles/CMakeTmp'