Determining if the pthread_create exist failed with the following output:
Change Dir: /home/casaburf/B1/B1-build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_32c2b/fast 
/usr/bin/gmake -f CMakeFiles/cmTC_32c2b.dir/build.make CMakeFiles/cmTC_32c2b.dir/build
gmake[1]: Entering directory `/home/casaburf/B1/B1-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_32c2b.dir/CheckSymbolExists.c.o
/cvmfs/sft.cern.ch/lcg/releases/gcc/8.3.0-cebb0/x86_64-centos7/bin/gcc    -o CMakeFiles/cmTC_32c2b.dir/CheckSymbolExists.c.o   -c /home/casaburf/B1/B1-build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_32c2b
/cvmfs/sft.cern.ch/lcg/contrib/CMake/3.14.2/Linux-x86_64/bin/cmake -E cmake_link_script CMakeFiles/cmTC_32c2b.dir/link.txt --verbose=1
/cvmfs/sft.cern.ch/lcg/releases/gcc/8.3.0-cebb0/x86_64-centos7/bin/gcc      CMakeFiles/cmTC_32c2b.dir/CheckSymbolExists.c.o  -o cmTC_32c2b 
CMakeFiles/cmTC_32c2b.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text+0x16): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
gmake[1]: *** [cmTC_32c2b] Error 1
gmake[1]: Leaving directory `/home/casaburf/B1/B1-build/CMakeFiles/CMakeTmp'
gmake: *** [cmTC_32c2b/fast] Error 2

File /home/casaburf/B1/B1-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
}