cmake PLIBSYS_HAS_POSIX_STACKSIZE examples

saprykin/plibsys src/CMakeLists.txt :541

check_c_source_compiles (
                                 "#include <pthread.h>

                                 int main () {
                                        pthread_attr_t attr;

                                        pthread_attr_setstacksize (&attr, 0);
                                        return 0;
                                 }"
                                 PLIBSYS_HAS_POSIX_STACKSIZE
                                )