Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_b760c/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_b760c.dir/build.make CMakeFiles/cmTC_b760c.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_b760c.dir/src.c.o
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/aarch64-linux-gnu-gcc --sysroot=/home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot -D_GNU_SOURCE -D_POSIX_C_SOURCE=200809L -D__BSD_VISIBLE=1  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -D_FORTIFY_SOURCE=2 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_b760c.dir/src.c.o   -c /home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_b760c
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_b760c.dir/link.txt --verbose=1
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/aarch64-linux-gnu-gcc --sysroot=/home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -D_FORTIFY_SOURCE=2 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_b760c.dir/src.c.o  -o cmTC_b760c /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libssl.so /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libcrypto.so /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libssh.so /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libnetconf2.so 
/home/buildroot/autobuild/run/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/7.3.1/../../../../aarch64-linux-gnu/bin/ld: CMakeFiles/cmTC_b760c.dir/src.c.o: undefined reference to symbol 'pthread_join@@GLIBC_2.17'
/home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/lib64/libpthread.so.0: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_b760c] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_b760c/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/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/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_57563/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_57563.dir/build.make CMakeFiles/cmTC_57563.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_57563.dir/CheckFunctionExists.c.o
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/aarch64-linux-gnu-gcc --sysroot=/home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot -D_GNU_SOURCE -D_POSIX_C_SOURCE=200809L -D__BSD_VISIBLE=1  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -D_FORTIFY_SOURCE=2 -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_57563.dir/CheckFunctionExists.c.o   -c /home/buildroot/autobuild/run/instance-1/output-1/host/share/cmake-3.15/Modules/CheckFunctionExists.c
Linking C executable cmTC_57563
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_57563.dir/link.txt --verbose=1
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/aarch64-linux-gnu-gcc --sysroot=/home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -D_FORTIFY_SOURCE=2 -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_57563.dir/CheckFunctionExists.c.o  -o cmTC_57563 -lpthreads /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libssl.so /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libcrypto.so /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libssh.so /home/buildroot/autobuild/run/instance-1/output-1/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libnetconf2.so 
/home/buildroot/autobuild/run/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/7.3.1/../../../../aarch64-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_57563] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_57563/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/build/netopeer2-1.1.53/CMakeFiles/CMakeTmp'