Determining if the pthread_create exist failed with the following output:
Change Dir: /home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/gmake" "cmTC_e7efe/fast"
gmake[1]: Entering directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
/usr/bin/gmake -f CMakeFiles/cmTC_e7efe.dir/build.make CMakeFiles/cmTC_e7efe.dir/build
gmake[2]: Entering directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_e7efe.dir/CheckSymbolExists.c.o
/home/naourr/work/instance-1/output/host/bin/aarch64_be-linux-gnu-gcc --sysroot=/home/naourr/work/instance-1/output/host/aarch64_be-buildroot-linux-gnu/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -std=gnu99 -fvisibility=hidden -Wsign-compare -Wall -Wno-uninitialized   -DNDEBUG   -o CMakeFiles/cmTC_e7efe.dir/CheckSymbolExists.c.o   -c /home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_e7efe
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_e7efe.dir/link.txt --verbose=1
/home/naourr/work/instance-1/output/host/bin/aarch64_be-linux-gnu-gcc --sysroot=/home/naourr/work/instance-1/output/host/aarch64_be-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -std=gnu99 -fvisibility=hidden -Wsign-compare -Wall -Wno-uninitialized   -DNDEBUG    -rdynamic CMakeFiles/cmTC_e7efe.dir/CheckSymbolExists.c.o  -o cmTC_e7efe 
CMakeFiles/cmTC_e7efe.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text.startup+0x0): undefined reference to `pthread_create'
CheckSymbolExists.c:(.text.startup+0x4): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
gmake[2]: *** [CMakeFiles/cmTC_e7efe.dir/build.make:87: cmTC_e7efe] Error 1
gmake[2]: Leaving directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
gmake[1]: *** [Makefile:126: cmTC_e7efe/fast] Error 2
gmake[1]: Leaving directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'

File /home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <pthread.h>

int main(int argc, char** argv)
{
  (void)argv;
#ifndef pthread_create
  return ((int*)(&pthread_create))[argc];
#else
  (void)argc;
  return 0;
#endif
}

Determining if the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/gmake" "cmTC_0691d/fast"
gmake[1]: Entering directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
/usr/bin/gmake -f CMakeFiles/cmTC_0691d.dir/build.make CMakeFiles/cmTC_0691d.dir/build
gmake[2]: Entering directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_0691d.dir/CheckFunctionExists.c.o
/home/naourr/work/instance-1/output/host/bin/aarch64_be-linux-gnu-gcc --sysroot=/home/naourr/work/instance-1/output/host/aarch64_be-buildroot-linux-gnu/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -std=gnu99 -fvisibility=hidden -Wsign-compare -Wall -Wno-uninitialized -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_0691d.dir/CheckFunctionExists.c.o   -c /usr/share/cmake/Modules/CheckFunctionExists.c
Linking C executable cmTC_0691d
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_0691d.dir/link.txt --verbose=1
/home/naourr/work/instance-1/output/host/bin/aarch64_be-linux-gnu-gcc --sysroot=/home/naourr/work/instance-1/output/host/aarch64_be-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -std=gnu99 -fvisibility=hidden -Wsign-compare -Wall -Wno-uninitialized -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    -rdynamic CMakeFiles/cmTC_0691d.dir/CheckFunctionExists.c.o  -o cmTC_0691d -lpthreads 
/home/naourr/work/instance-1/output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64_be-linux-gnu/7.3.1/../../../../aarch64_be-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
gmake[2]: *** [CMakeFiles/cmTC_0691d.dir/build.make:87: cmTC_0691d] Error 1
gmake[2]: Leaving directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
gmake[1]: *** [Makefile:126: cmTC_0691d/fast] Error 2
gmake[1]: Leaving directory '/home/naourr/work/instance-1/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'