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_a2bca/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_a2bca.dir/build.make CMakeFiles/cmTC_a2bca.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_a2bca.dir/src.cxx.o
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/nios2-linux-gnu-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/nios2-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_a2bca.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_a2bca
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_a2bca.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/nios2-linux-gnu-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/nios2-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_a2bca.dir/src.cxx.o  -o cmTC_a2bca 
CMakeFiles/cmTC_a2bca.dir/src.cxx.o: In function `main':
src.cxx:(.text.startup+0x1c): undefined reference to `pthread_create'
src.cxx:(.text.startup+0x24): undefined reference to `pthread_detach'
src.cxx:(.text.startup+0x30): undefined reference to `pthread_join'
src.cxx:(.text.startup+0x40): undefined reference to `pthread_atfork'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_a2bca.dir/build.make:87: cmTC_a2bca] 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_a2bca/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_71d9a/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_71d9a.dir/build.make CMakeFiles/cmTC_71d9a.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_71d9a.dir/CheckFunctionExists.cxx.o
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/nios2-linux-gnu-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/nios2-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_71d9a.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_71d9a
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_71d9a.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/bin/nios2-linux-gnu-g++ --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/nios2-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_71d9a.dir/CheckFunctionExists.cxx.o  -o cmTC_71d9a  -lpthreads 
/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/nios2-linux-gnu/7.3.1/../../../../nios2-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_71d9a.dir/build.make:87: cmTC_71d9a] 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_71d9a/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-1/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'