Performing C++ SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_fdfa6/fast && make[1]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_fdfa6.dir/build.make CMakeFiles/cmTC_fdfa6.dir/build
make[2]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_fdfa6.dir/src.cxx.o
/srv/storage/autobuild/run/instance-0/output-1/host/bin/riscv32-linux-g++ --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/riscv32-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_fdfa6.dir/src.cxx.o -c /srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp/src.cxx
Linking CXX executable cmTC_fdfa6
/srv/storage/autobuild/run/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_fdfa6.dir/link.txt --verbose=1
/srv/storage/autobuild/run/instance-0/output-1/host/bin/riscv32-linux-g++ --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/riscv32-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_fdfa6.dir/src.cxx.o  -o cmTC_fdfa6 
/srv/storage/autobuild/run/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/riscv32-buildroot-linux-gnu/8.3.0/../../../../riscv32-buildroot-linux-gnu/bin/ld: CMakeFiles/cmTC_fdfa6.dir/src.cxx.o: in function `.L0 ':
src.cxx:(.text.startup+0x2c): undefined reference to `pthread_create'
/srv/storage/autobuild/run/instance-0/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'
/srv/storage/autobuild/run/instance-0/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+0x40): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_fdfa6.dir/build.make:87: cmTC_fdfa6] Error 1
make[2]: Leaving directory '/srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:121: cmTC_fdfa6/fast] Error 2
make[1]: Leaving directory '/srv/storage/autobuild/run/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: /srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_fdfaf/fast && make[1]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_fdfaf.dir/build.make CMakeFiles/cmTC_fdfaf.dir/build
make[2]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_fdfaf.dir/CheckFunctionExists.cxx.o
/srv/storage/autobuild/run/instance-0/output-1/host/bin/riscv32-linux-g++ --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/riscv32-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_fdfaf.dir/CheckFunctionExists.cxx.o -c /srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CheckLibraryExists/CheckFunctionExists.cxx
Linking CXX executable cmTC_fdfaf
/srv/storage/autobuild/run/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_fdfaf.dir/link.txt --verbose=1
/srv/storage/autobuild/run/instance-0/output-1/host/bin/riscv32-linux-g++ --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/riscv32-buildroot-linux-gnu/sysroot  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_fdfaf.dir/CheckFunctionExists.cxx.o  -o cmTC_fdfaf -lpthreads 
/srv/storage/autobuild/run/instance-0/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_fdfaf.dir/build.make:87: cmTC_fdfaf] Error 1
make[2]: Leaving directory '/srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:121: cmTC_fdfaf/fast] Error 2
make[1]: Leaving directory '/srv/storage/autobuild/run/instance-0/output-1/build/libabseil-cpp-20200225/CMakeFiles/CMakeTmp'