Determining if the pthread_create exist failed with the following output:
Change Dir: /accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_ac045/fast"
make[1]: Entering directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_ac045.dir/build.make CMakeFiles/cmTC_ac045.dir/build
make[2]: Entering directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_ac045.dir/CheckSymbolExists.c.o
/accts/mlweber1/instance-3/output/host/bin/aarch64-linux-gcc --sysroot=/accts/mlweber1/instance-3/output/host/aarch64-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_ac045.dir/CheckSymbolExists.c.o   -c /accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_ac045
/accts/mlweber1/instance-3/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_ac045.dir/link.txt --verbose=1
/accts/mlweber1/instance-3/output/host/bin/aarch64-linux-gcc --sysroot=/accts/mlweber1/instance-3/output/host/aarch64-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_ac045.dir/CheckSymbolExists.c.o  -o cmTC_ac045 
CMakeFiles/cmTC_ac045.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
make[2]: *** [cmTC_ac045] Error 1
make[2]: Leaving directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_ac045/fast] Error 2
make[1]: Leaving directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'

File /accts/mlweber1/instance-3/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: /accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_bbad7/fast"
make[1]: Entering directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_bbad7.dir/build.make CMakeFiles/cmTC_bbad7.dir/build
make[2]: Entering directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_bbad7.dir/CheckFunctionExists.c.o
/accts/mlweber1/instance-3/output/host/bin/aarch64-linux-gcc --sysroot=/accts/mlweber1/instance-3/output/host/aarch64-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_bbad7.dir/CheckFunctionExists.c.o   -c /accts/mlweber1/instance-3/output/host/share/cmake-3.8/Modules/CheckFunctionExists.c
Linking C executable cmTC_bbad7
/accts/mlweber1/instance-3/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_bbad7.dir/link.txt --verbose=1
/accts/mlweber1/instance-3/output/host/bin/aarch64-linux-gcc --sysroot=/accts/mlweber1/instance-3/output/host/aarch64-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_bbad7.dir/CheckFunctionExists.c.o  -o cmTC_bbad7 -lpthreads 
/accts/mlweber1/instance-3/output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-buildroot-linux-gnu/6.4.0/../../../../aarch64-buildroot-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_bbad7] Error 1
make[2]: Leaving directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_bbad7/fast] Error 2
make[1]: Leaving directory `/accts/mlweber1/instance-3/output/build/gnuradio-3.7.13.3/buildroot-build/CMakeFiles/CMakeTmp'