Performing C SOURCE FILE Test CMAKE_HAVE_LIBC_PTHREAD failed with the following output:
Change Dir: /home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_da4f5/fast && make[1]: Entering directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_da4f5.dir/build.make CMakeFiles/cmTC_da4f5.dir/build
make[2]: Entering directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_da4f5.dir/src.c.o
/home/buildroot/autobuild/instance-0/output-1/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/buildroot/autobuild/instance-0/output-1/host/arm-buildroot-linux-gnueabi/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG   -o CMakeFiles/cmTC_da4f5.dir/src.c.o   -c /home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp/src.c
Linking C executable cmTC_da4f5
/home/buildroot/autobuild/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_da4f5.dir/link.txt --verbose=1
/home/buildroot/autobuild/instance-0/output-1/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/buildroot/autobuild/instance-0/output-1/host/arm-buildroot-linux-gnueabi/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCMAKE_HAVE_LIBC_PTHREAD  -DNDEBUG    CMakeFiles/cmTC_da4f5.dir/src.c.o  -o cmTC_da4f5 
CMakeFiles/cmTC_da4f5.dir/src.c.o: In function `main':
src.c:(.text.startup+0x10): undefined reference to `pthread_create'
src.c:(.text.startup+0x16): undefined reference to `pthread_detach'
src.c:(.text.startup+0x1e): undefined reference to `pthread_join'
src.c:(.text.startup+0x28): undefined reference to `pthread_atfork'
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_da4f5.dir/build.make:86: recipe for target 'cmTC_da4f5' failed
make[2]: *** [cmTC_da4f5] Error 1
make[2]: Leaving directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp'
Makefile:121: recipe for target 'cmTC_da4f5/fast' failed
make[1]: *** [cmTC_da4f5/fast] Error 2
make[1]: Leaving directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/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/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_803a7/fast && make[1]: Entering directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_803a7.dir/build.make CMakeFiles/cmTC_803a7.dir/build
make[2]: Entering directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_803a7.dir/CheckFunctionExists.c.o
/home/buildroot/autobuild/instance-0/output-1/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/buildroot/autobuild/instance-0/output-1/host/arm-buildroot-linux-gnueabi/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_803a7.dir/CheckFunctionExists.c.o   -c /home/buildroot/autobuild/instance-0/output-1/host/share/cmake-3.15/Modules/CheckFunctionExists.c
Linking C executable cmTC_803a7
/home/buildroot/autobuild/instance-0/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_803a7.dir/link.txt --verbose=1
/home/buildroot/autobuild/instance-0/output-1/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/buildroot/autobuild/instance-0/output-1/host/arm-buildroot-linux-gnueabi/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_803a7.dir/CheckFunctionExists.c.o  -o cmTC_803a7 -lpthreads 
/home/buildroot/autobuild/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/arm-none-linux-gnueabi/4.8.3/../../../../arm-none-linux-gnueabi/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_803a7.dir/build.make:86: recipe for target 'cmTC_803a7' failed
make[2]: *** [cmTC_803a7] Error 1
make[2]: Leaving directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp'
Makefile:121: recipe for target 'cmTC_803a7/fast' failed
make[1]: *** [cmTC_803a7/fast] Error 2
make[1]: Leaving directory '/home/buildroot/autobuild/instance-0/output-1/build/optee-client-3.11.0/CMakeFiles/CMakeTmp'