Determining if the pthread_create exist failed with the following output:
Change Dir: /home/alexis/dfhack-0.47.03-alpha0/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/ninja" "cmTC_2cf74"
[1/2] Building C object CMakeFiles/cmTC_2cf74.dir/CheckSymbolExists.c.o
[2/2] Linking C executable cmTC_2cf74
FAILED: cmTC_2cf74
: && /usr/bin/cc -fvisibility=hidden -mtune=generic -m64 -mno-avx  -rdynamic CMakeFiles/cmTC_2cf74.dir/CheckSymbolExists.c.o  -o cmTC_2cf74   && :
CMakeFiles/cmTC_2cf74.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text+0x1b): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

File /home/alexis/dfhack-0.47.03-alpha0/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/alexis/dfhack-0.47.03-alpha0/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/ninja" "cmTC_b7266"
[1/2] Building C object CMakeFiles/cmTC_b7266.dir/CheckFunctionExists.c.o
[2/2] Linking C executable cmTC_b7266
FAILED: cmTC_b7266
: && /usr/bin/cc -fvisibility=hidden -mtune=generic -m64 -mno-avx -DCHECK_FUNCTION_EXISTS=pthread_create  -rdynamic CMakeFiles/cmTC_b7266.dir/CheckFunctionExists.c.o  -o cmTC_b7266  -lpthreads && :
/usr/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.