cmake HAVE_PTHREAD_T_POINTER examples

JulNadeauCA/libagar CMakeChecks.cmake :2406

check_c_source_compiles("
#include <pthread.h>
static void *start_routine(void *arg) { return (NULL); }
int main(int argc, char *argv[])
{
	pthread_t th = NULL;
	return pthread_create(&th, NULL, start_routine, NULL);
}
" HAVE_PTHREAD_T_POINTER)