Determining if the pthread_create exist failed with the following output:
Change Dir: /home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_7ef1c/fast"
make[1]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_7ef1c.dir/build.make CMakeFiles/cmTC_7ef1c.dir/build
make[2]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_7ef1c.dir/CheckSymbolExists.c.o
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-gcc  --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/powerpc-buildroot-linux-gnuspe/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -mabi=spe -mfloat-gprs=double -Wa,-me500x2 -Os   -DNDEBUG   -o CMakeFiles/cmTC_7ef1c.dir/CheckSymbolExists.c.o   -c /home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_7ef1c
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_7ef1c.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-gcc  --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/powerpc-buildroot-linux-gnuspe/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -mabi=spe -mfloat-gprs=double -Wa,-me500x2 -Os   -DNDEBUG    CMakeFiles/cmTC_7ef1c.dir/CheckSymbolExists.c.o  -o cmTC_7ef1c -rdynamic 
CMakeFiles/cmTC_7ef1c.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text.startup+0x2): undefined reference to `pthread_create'
CheckSymbolExists.c:(.text.startup+0xa): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_7ef1c.dir/build.make:97: recipe for target 'cmTC_7ef1c' failed
make[2]: *** [cmTC_7ef1c] Error 1
make[2]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_7ef1c/fast' failed
make[1]: *** [cmTC_7ef1c/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'

File /home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/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/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_9916b/fast"
make[1]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_9916b.dir/build.make CMakeFiles/cmTC_9916b.dir/build
make[2]: Entering directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_9916b.dir/CheckFunctionExists.c.o
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-gcc  --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/powerpc-buildroot-linux-gnuspe/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -mabi=spe -mfloat-gprs=double -Wa,-me500x2 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG   -o CMakeFiles/cmTC_9916b.dir/CheckFunctionExists.c.o   -c /usr/share/cmake-3.5/Modules/CheckFunctionExists.c
Linking C executable cmTC_9916b
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_9916b.dir/link.txt --verbose=1
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-gcc  --sysroot=/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/powerpc-buildroot-linux-gnuspe/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -mabi=spe -mfloat-gprs=double -Wa,-me500x2 -Os -DCHECK_FUNCTION_EXISTS=pthread_create  -DNDEBUG    CMakeFiles/cmTC_9916b.dir/CheckFunctionExists.c.o  -o cmTC_9916b -rdynamic -lpthreads 
/home/rclinux/rc-buildroot-test/scripts/instance-0/output/host/opt/ext-toolchain/bin/../lib/gcc/powerpc-ctng_e500v2-linux-gnuspe/4.7.3/../../../../powerpc-ctng_e500v2-linux-gnuspe/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_9916b.dir/build.make:97: recipe for target 'cmTC_9916b' failed
make[2]: *** [cmTC_9916b] Error 1
make[2]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_9916b/fast' failed
make[1]: *** [cmTC_9916b/fast] Error 2
make[1]: Leaving directory '/home/rclinux/rc-buildroot-test/scripts/instance-0/output/build/libcpprestsdk-v2.10.8/Release/CMakeFiles/CMakeTmp'