Determining if the pthread_setname_np exist failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_a4794/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_a4794.dir/build.make CMakeFiles/cmTC_a4794.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_a4794.dir/CheckSymbolExists.c.o
/usr/bin/gcc   -O2 -I/home/buildroot/autobuild/run/instance-0/output-1/host/include  -fPIE   -o CMakeFiles/cmTC_a4794.dir/CheckSymbolExists.c.o   -c /home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c
/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c: In function 'main':
/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8:19: error: 'pthread_setname_np' undeclared (first use in this function)
   return ((int*)(&pthread_setname_np))[argc];
                   ^
/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8:19: note: each undeclared identifier is reported only once for each function it appears in
make[2]: *** [CMakeFiles/cmTC_a4794.dir/CheckSymbolExists.c.o] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_a4794/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'


File /home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <pthread.h>

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

Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_4ae5c/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_4ae5c.dir/build.make CMakeFiles/cmTC_4ae5c.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_4ae5c.dir/src.c.o
/usr/bin/gcc   -O2 -I/home/buildroot/autobuild/run/instance-0/output-1/host/include  -DCMAKE_HAVE_LIBC_PTHREAD -fPIE   -o CMakeFiles/cmTC_4ae5c.dir/src.c.o   -c /home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_4ae5c
/home/buildroot/autobuild/run/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_4ae5c.dir/link.txt --verbose=1
/usr/bin/gcc -O2 -I/home/buildroot/autobuild/run/instance-0/output-1/host/include  -DCMAKE_HAVE_LIBC_PTHREAD  -L/home/buildroot/autobuild/run/instance-0/output-1/host/lib -Wl,-rpath,/home/buildroot/autobuild/run/instance-0/output-1/host/lib  CMakeFiles/cmTC_4ae5c.dir/src.c.o  -o cmTC_4ae5c 
CMakeFiles/cmTC_4ae5c.dir/src.c.o: In function `main':
src.c:(.text.startup+0x15): undefined reference to `pthread_create'
src.c:(.text.startup+0x1f): undefined reference to `pthread_detach'
src.c:(.text.startup+0x2b): undefined reference to `pthread_join'
src.c:(.text.startup+0x36): undefined reference to `pthread_atfork'
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_4ae5c] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_4ae5c/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'


Source file was:
#include <pthread.h>

void* test_func(void* data)
{
  return data;
}

int main(void)
{
  pthread_t thread;
  pthread_create(&thread, NULL, test_func, NULL);
  pthread_detach(thread);
  pthread_join(thread, NULL);
  pthread_atfork(NULL, NULL, NULL);
  pthread_exit(NULL);

  return 0;
}

Determining if the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_6a4dc/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_6a4dc.dir/build.make CMakeFiles/cmTC_6a4dc.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_6a4dc.dir/CheckFunctionExists.c.o
/usr/bin/gcc   -O2 -I/home/buildroot/autobuild/run/instance-0/output-1/host/include  -DCHECK_FUNCTION_EXISTS=pthread_create -fPIE   -o CMakeFiles/cmTC_6a4dc.dir/CheckFunctionExists.c.o   -c /home/buildroot/autobuild/run/instance-0/output-1/host/share/cmake-3.15/Modules/CheckFunctionExists.c
Linking C executable cmTC_6a4dc
/home/buildroot/autobuild/run/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_6a4dc.dir/link.txt --verbose=1
/usr/bin/gcc -O2 -I/home/buildroot/autobuild/run/instance-0/output-1/host/include  -DCHECK_FUNCTION_EXISTS=pthread_create  -L/home/buildroot/autobuild/run/instance-0/output-1/host/lib -Wl,-rpath,/home/buildroot/autobuild/run/instance-0/output-1/host/lib  CMakeFiles/cmTC_6a4dc.dir/CheckFunctionExists.c.o  -o cmTC_6a4dc -lpthreads 
/usr/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_6a4dc] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_6a4dc/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-0/output-1/build/host-grpc-1.25.0/CMakeFiles/CMakeTmp'