Determining if the pthread_setname_np exist failed with the following output:
Change Dir: /home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_9aa7b/fast && make[1]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_9aa7b.dir/build.make CMakeFiles/cmTC_9aa7b.dir/build
make[2]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_9aa7b.dir/CheckSymbolExists.c.o
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os   -DNDEBUG -fPIE   -o CMakeFiles/cmTC_9aa7b.dir/CheckSymbolExists.c.o   -c /home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c: In function 'main':
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8:19: error: 'pthread_setname_np' undeclared (first use in this function)
   return ((int*)(&pthread_setname_np))[argc];
                   ^
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8:19: note: each undeclared identifier is reported only once for each function it appears in
CMakeFiles/cmTC_9aa7b.dir/build.make:65: recipe for target 'CMakeFiles/cmTC_9aa7b.dir/CheckSymbolExists.c.o' failed
make[2]: *** [CMakeFiles/cmTC_9aa7b.dir/CheckSymbolExists.c.o] Error 1
make[2]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
Makefile:121: recipe for target 'cmTC_9aa7b/fast' failed
make[1]: *** [cmTC_9aa7b/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'


File /home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/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/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_1c3a2/fast && make[1]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_1c3a2.dir/build.make CMakeFiles/cmTC_1c3a2.dir/build
make[2]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_1c3a2.dir/src.c.o
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG -fPIE   -o CMakeFiles/cmTC_1c3a2.dir/src.c.o   -c /home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_1c3a2
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_1c3a2.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG  -latomic  CMakeFiles/cmTC_1c3a2.dir/src.c.o  -o cmTC_1c3a2 
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-none-linux-gnueabi/4.8.3/../../../../arm-none-linux-gnueabi/bin/ld: CMakeFiles/cmTC_1c3a2.dir/src.c.o: undefined reference to symbol 'pthread_join@@GLIBC_2.4'
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot/lib/libpthread.so.0: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_1c3a2.dir/build.make:86: recipe for target 'cmTC_1c3a2' failed
make[2]: *** [cmTC_1c3a2] Error 1
make[2]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
Makefile:121: recipe for target 'cmTC_1c3a2/fast' failed
make[1]: *** [cmTC_1c3a2/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/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/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_5916a/fast && make[1]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_5916a.dir/build.make CMakeFiles/cmTC_5916a.dir/build
make[2]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_5916a.dir/CheckFunctionExists.c.o
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG -fPIE   -o CMakeFiles/cmTC_5916a.dir/CheckFunctionExists.c.o   -c /home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/share/cmake-3.15/Modules/CheckFunctionExists.c
Linking C executable cmTC_5916a
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_5916a.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG  -latomic  CMakeFiles/cmTC_5916a.dir/CheckFunctionExists.c.o  -o cmTC_5916a -lpthreads 
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-none-linux-gnueabi/4.8.3/../../../../arm-none-linux-gnueabi/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_5916a.dir/build.make:86: recipe for target 'cmTC_5916a' failed
make[2]: *** [cmTC_5916a] Error 1
make[2]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'
Makefile:121: recipe for target 'cmTC_5916a/fast' failed
make[1]: *** [cmTC_5916a/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/grpc-1.23.0/CMakeFiles/CMakeTmp'