Determining if the pthread_create exist failed with the following output:
Change Dir: /content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_299c9/fast"
make[3]: Entering directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_299c9.dir/build.make CMakeFiles/cmTC_299c9.dir/build
make[4]: Entering directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_299c9.dir/CheckSymbolExists.c.o
/usr/bin/cc    -o CMakeFiles/cmTC_299c9.dir/CheckSymbolExists.c.o   -c /content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_299c9
/usr/local/bin/cmake -E cmake_link_script CMakeFiles/cmTC_299c9.dir/link.txt --verbose=1
/usr/bin/cc      -rdynamic CMakeFiles/cmTC_299c9.dir/CheckSymbolExists.c.o  -o cmTC_299c9 
/usr/bin/ld: CMakeFiles/cmTC_299c9.dir/CheckSymbolExists.c.o: in function `main':
CheckSymbolExists.c:(.text+0x1f): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
make[4]: *** [CMakeFiles/cmTC_299c9.dir/build.make:87: cmTC_299c9] Error 1
make[4]: Leaving directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'
make[3]: *** [Makefile:121: cmTC_299c9/fast] Error 2
make[3]: Leaving directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'

File /content/openpose/build/caffe/src/openpose_lib-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: /content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_5d59b/fast"
make[3]: Entering directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_5d59b.dir/build.make CMakeFiles/cmTC_5d59b.dir/build
make[4]: Entering directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_5d59b.dir/CheckFunctionExists.c.o
/usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create   -o CMakeFiles/cmTC_5d59b.dir/CheckFunctionExists.c.o   -c /usr/local/share/cmake-3.13/Modules/CheckFunctionExists.c
Linking C executable cmTC_5d59b
/usr/local/bin/cmake -E cmake_link_script CMakeFiles/cmTC_5d59b.dir/link.txt --verbose=1
/usr/bin/cc  -DCHECK_FUNCTION_EXISTS=pthread_create    -rdynamic CMakeFiles/cmTC_5d59b.dir/CheckFunctionExists.c.o  -o cmTC_5d59b -lpthreads 
/usr/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[4]: *** [CMakeFiles/cmTC_5d59b.dir/build.make:87: cmTC_5d59b] Error 1
make[4]: Leaving directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'
make[3]: *** [Makefile:121: cmTC_5d59b/fast] Error 2
make[3]: Leaving directory '/content/openpose/build/caffe/src/openpose_lib-build/CMakeFiles/CMakeTmp'