Performing C++ SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_c5bb2/fast && gmake[1]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
/usr/bin/gmake -f CMakeFiles/cmTC_c5bb2.dir/build.make CMakeFiles/cmTC_c5bb2.dir/build
gmake[2]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_c5bb2.dir/src.cxx.o
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/bin/nios2-linux-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/nios2-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_c5bb2.dir/src.cxx.o -c /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp/src.cxx
Linking CXX executable cmTC_c5bb2
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_c5bb2.dir/link.txt --verbose=1
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/bin/nios2-linux-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/nios2-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_c5bb2.dir/src.cxx.o  -o cmTC_c5bb2 
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/nios2-buildroot-linux-gnu/8.3.0/../../../../nios2-buildroot-linux-gnu/bin/ld: CMakeFiles/cmTC_c5bb2.dir/src.cxx.o: in function `main':
src.cxx:(.text.startup+0x1c): undefined reference to `pthread_create'
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/nios2-buildroot-linux-gnu/8.3.0/../../../../nios2-buildroot-linux-gnu/bin/ld: src.cxx:(.text.startup+0x24): undefined reference to `pthread_detach'
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/nios2-buildroot-linux-gnu/8.3.0/../../../../nios2-buildroot-linux-gnu/bin/ld: src.cxx:(.text.startup+0x30): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
gmake[2]: *** [cmTC_c5bb2] Error 1
gmake[2]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
gmake[1]: *** [cmTC_c5bb2/fast] Error 2
gmake[1]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/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: /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_88d30/fast && gmake[1]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
/usr/bin/gmake -f CMakeFiles/cmTC_88d30.dir/build.make CMakeFiles/cmTC_88d30.dir/build
gmake[2]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_88d30.dir/CheckFunctionExists.cxx.o
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/bin/nios2-linux-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/nios2-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_88d30.dir/CheckFunctionExists.cxx.o -c /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx
Linking CXX executable cmTC_88d30
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_88d30.dir/link.txt --verbose=1
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/bin/nios2-linux-g++ --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/nios2-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_88d30.dir/CheckFunctionExists.cxx.o  -o cmTC_88d30 -lpthreads 
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/nios2-buildroot-linux-gnu/8.3.0/../../../../nios2-buildroot-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
gmake[2]: *** [cmTC_88d30] Error 1
gmake[2]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
gmake[1]: *** [cmTC_88d30/fast] Error 2
gmake[1]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'