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/domoticz-2021.1/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_adb89/fast && make[1]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp'
/usr/bin/make  -f CMakeFiles/cmTC_adb89.dir/build.make CMakeFiles/cmTC_adb89.dir/build
make[2]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_adb89.dir/src.c.o
/srv/storage/autobuild/run/instance-0/output-1/host/bin/mips-linux-gnu-gcc --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/mips64el-buildroot-linux-gnu/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -D_FORTIFY_SOURCE=1 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_adb89.dir/src.c.o   -c /srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_adb89
/srv/storage/autobuild/run/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_adb89.dir/link.txt --verbose=1
/srv/storage/autobuild/run/instance-0/output-1/host/bin/mips-linux-gnu-gcc --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/mips64el-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -D_FORTIFY_SOURCE=1 -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_adb89.dir/src.c.o  -o cmTC_adb89 
CMakeFiles/cmTC_adb89.dir/src.c.o: In function `main':
src.c:(.text.startup+0x18): undefined reference to `pthread_create'
src.c:(.text.startup+0x28): undefined reference to `pthread_create'
src.c:(.text.startup+0x30): undefined reference to `pthread_detach'
src.c:(.text.startup+0x34): undefined reference to `pthread_detach'
src.c:(.text.startup+0x40): undefined reference to `pthread_join'
src.c:(.text.startup+0x44): undefined reference to `pthread_join'
src.c:(.text.startup+0x4c): undefined reference to `pthread_atfork'
src.c:(.text.startup+0x58): undefined reference to `pthread_atfork'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_adb89.dir/build.make:90: cmTC_adb89] Error 1
make[2]: Leaving directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:124: cmTC_adb89/fast] Error 2
make[1]: Leaving directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/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: /srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_d72c4/fast && make[1]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp'
/usr/bin/make  -f CMakeFiles/cmTC_d72c4.dir/build.make CMakeFiles/cmTC_d72c4.dir/build
make[2]: Entering directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_d72c4.dir/CheckFunctionExists.c.o
/srv/storage/autobuild/run/instance-0/output-1/host/bin/mips-linux-gnu-gcc --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/mips64el-buildroot-linux-gnu/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -D_FORTIFY_SOURCE=1 -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_d72c4.dir/CheckFunctionExists.c.o   -c /srv/storage/autobuild/run/instance-0/output-1/host/share/cmake-3.16/Modules/CheckFunctionExists.c
Linking C executable cmTC_d72c4
/srv/storage/autobuild/run/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_d72c4.dir/link.txt --verbose=1
/srv/storage/autobuild/run/instance-0/output-1/host/bin/mips-linux-gnu-gcc --sysroot=/srv/storage/autobuild/run/instance-0/output-1/host/mips64el-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -D_FORTIFY_SOURCE=1 -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_d72c4.dir/CheckFunctionExists.c.o  -o cmTC_d72c4  -lpthreads 
/srv/storage/autobuild/run/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/mips-linux-gnu/5.3.0/../../../../mips-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cmTC_d72c4.dir/build.make:90: cmTC_d72c4] Error 1
make[2]: Leaving directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:124: cmTC_d72c4/fast] Error 2
make[1]: Leaving directory '/srv/storage/autobuild/run/instance-0/output-1/build/domoticz-2021.1/CMakeFiles/CMakeTmp'