cmake HAVE_GETTID_SYSCALL examples

LiangliangNan/MVStudio 3rd_party/nlopt/CMakeLists.txt :117 

check_function_exists (syscall HAVE_GETTID_SYSCALL)

stevengj/nlopt CMakeLists.txt :94 

check_function_exists (syscall HAVE_GETTID_SYSCALL)