Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_113d5/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_113d5.dir/build.make CMakeFiles/cmTC_113d5.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_113d5.dir/src.c.o
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/arm-buildroot-linux-gnueabihf-gcc --sysroot=/home/buildroot/autobuild/run/instance-3/output-1/host/arm-buildroot-linux-gnueabihf/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_113d5.dir/src.c.o   -c /home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_113d5
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_113d5.dir/link.txt --verbose=1
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/arm-buildroot-linux-gnueabihf-gcc --sysroot=/home/buildroot/autobuild/run/instance-3/output-1/host/arm-buildroot-linux-gnueabihf/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_113d5.dir/src.c.o  -o cmTC_113d5 
/home/buildroot/autobuild/run/instance-3/output-1/host/lib/gcc/arm-buildroot-linux-gnueabihf/10.2.0/../../../../arm-buildroot-linux-gnueabihf/bin/ld: CMakeFiles/cmTC_113d5.dir/src.c.o: in function `main':
src.c:(.text.startup+0x24): undefined reference to `pthread_create'
/home/buildroot/autobuild/run/instance-3/output-1/host/lib/gcc/arm-buildroot-linux-gnueabihf/10.2.0/../../../../arm-buildroot-linux-gnueabihf/bin/ld: src.c:(.text.startup+0x2c): undefined reference to `pthread_detach'
/home/buildroot/autobuild/run/instance-3/output-1/host/lib/gcc/arm-buildroot-linux-gnueabihf/10.2.0/../../../../arm-buildroot-linux-gnueabihf/bin/ld: src.c:(.text.startup+0x38): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_113d5] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_113d5/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/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-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_a9bff/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_a9bff.dir/build.make CMakeFiles/cmTC_a9bff.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_a9bff.dir/CheckFunctionExists.c.o
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/arm-buildroot-linux-gnueabihf-gcc --sysroot=/home/buildroot/autobuild/run/instance-3/output-1/host/arm-buildroot-linux-gnueabihf/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_a9bff.dir/CheckFunctionExists.c.o   -c /home/buildroot/autobuild/run/instance-3/output-1/host/share/cmake-3.15/Modules/CheckFunctionExists.c
Linking C executable cmTC_a9bff
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_a9bff.dir/link.txt --verbose=1
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/arm-buildroot-linux-gnueabihf-gcc --sysroot=/home/buildroot/autobuild/run/instance-3/output-1/host/arm-buildroot-linux-gnueabihf/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_a9bff.dir/CheckFunctionExists.c.o  -o cmTC_a9bff -lpthreads 
/home/buildroot/autobuild/run/instance-3/output-1/host/lib/gcc/arm-buildroot-linux-gnueabihf/10.2.0/../../../../arm-buildroot-linux-gnueabihf/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_a9bff] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_a9bff/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/domoticz-2020.1/CMakeFiles/CMakeTmp'