cmake: really fix detection of pthread_setname_np() on Apple platforms.

cmake/sdlchecks.cmake

@@ -873,9 +873,9 @@ macro(CheckPTHREAD)
             #include <pthread.h>
             int main(int argc, char **argv) {
               #ifdef __APPLE__
-              pthread_setname_np(pthread_self());
+              pthread_setname_np(\"\");
               #else
-              pthread_setname_np(pthread_self(), \"\");
+              pthread_setname_np(pthread_self(),\"\");
               #endif
               return 0;
             }" HAVE_PTHREAD_SETNAME_NP)