Determining if the pthread_create exist failed with the following output:
Change Dir: /accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_35b51/fast"
make[1]: Entering directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_35b51.dir/build.make CMakeFiles/cmTC_35b51.dir/build
make[2]: Entering directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_35b51.dir/CheckSymbolExists.c.o
/usr/bin/gcc   -O2 -I/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/host/include  -fPIE   -o CMakeFiles/cmTC_35b51.dir/CheckSymbolExists.c.o   -c /accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_35b51
/usr/local/bin/cmake -E cmake_link_script CMakeFiles/cmTC_35b51.dir/link.txt --verbose=1
/usr/bin/gcc -O2 -I/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/host/include     -rdynamic CMakeFiles/cmTC_35b51.dir/CheckSymbolExists.c.o  -o cmTC_35b51 
CMakeFiles/cmTC_35b51.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text.startup+0x3): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_35b51] Error 1
make[2]: Leaving directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_35b51/fast] Error 2
make[1]: Leaving directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'

File /accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/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: /accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_5de6b/fast"
make[1]: Entering directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_5de6b.dir/build.make CMakeFiles/cmTC_5de6b.dir/build
make[2]: Entering directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_5de6b.dir/CheckFunctionExists.c.o
/usr/bin/gcc   -O2 -I/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/host/include -DCHECK_FUNCTION_EXISTS=pthread_create -fPIE   -o CMakeFiles/cmTC_5de6b.dir/CheckFunctionExists.c.o   -c /usr/local/share/cmake-3.9/Modules/CheckFunctionExists.c
Linking C executable cmTC_5de6b
/usr/local/bin/cmake -E cmake_link_script CMakeFiles/cmTC_5de6b.dir/link.txt --verbose=1
/usr/bin/gcc -O2 -I/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/host/include -DCHECK_FUNCTION_EXISTS=pthread_create    -rdynamic CMakeFiles/cmTC_5de6b.dir/CheckFunctionExists.c.o  -o cmTC_5de6b -lpthreads 
/usr/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_5de6b] Error 1
make[2]: Leaving directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_5de6b/fast] Error 2
make[1]: Leaving directory `/accts/mlweber1/rclinux/rc-buildroot-test/scripts/instance-1/output/build/host-grpc-v1.16.1/CMakeFiles/CMakeTmp'