Performing C++ SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_3c415/fast && make[1]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_3c415.dir/build.make CMakeFiles/cmTC_3c415.dir/build
make[2]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_3c415.dir/src.cxx.o
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/riscv32-linux-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/riscv32-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_3c415.dir/src.cxx.o -c /home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp/src.cxx
Linking CXX executable cmTC_3c415
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_3c415.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/riscv32-linux-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/riscv32-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_3c415.dir/src.cxx.o  -o cmTC_3c415 
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/riscv32-buildroot-linux-gnu/8.3.0/../../../../riscv32-buildroot-linux-gnu/bin/ld: CMakeFiles/cmTC_3c415.dir/src.cxx.o: in function `.L0 ':
src.cxx:(.text.startup+0x28): undefined reference to `pthread_create'
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/riscv32-buildroot-linux-gnu/8.3.0/../../../../riscv32-buildroot-linux-gnu/bin/ld: src.cxx:(.text.startup+0x34): undefined reference to `pthread_detach'
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/riscv32-buildroot-linux-gnu/8.3.0/../../../../riscv32-buildroot-linux-gnu/bin/ld: src.cxx:(.text.startup+0x44): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_3c415.dir/build.make:87: cmTC_3c415] Error 1
make[2]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:121: cmTC_3c415/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/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-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_9735d/fast && make[1]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_9735d.dir/build.make CMakeFiles/cmTC_9735d.dir/build
make[2]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_9735d.dir/CheckFunctionExists.cxx.o
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/riscv32-linux-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/riscv32-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_9735d.dir/CheckFunctionExists.cxx.o -c /home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx
Linking CXX executable cmTC_9735d
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_9735d.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/riscv32-linux-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/riscv32-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_9735d.dir/CheckFunctionExists.cxx.o  -o cmTC_9735d  -lpthreads 
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/riscv32-buildroot-linux-gnu/8.3.0/../../../../riscv32-buildroot-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_9735d.dir/build.make:87: cmTC_9735d] Error 1
make[2]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:121: cmTC_9735d/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'