player: log if NDEBUG is defined

I sure want to know whether assert()s were unexpectedly not compiled in.

player/main.c

@@ -149,6 +149,9 @@ void mp_print_version(struct mp_log *log, int always)
     if (!always) {
         mp_msg(log, MSGL_V, "Configuration: " CONFIGURATION "\n");
         mp_msg(log, MSGL_V, "List of enabled features: %s\n", FULLCONFIG);
+        #ifdef NDEBUGs
+            mp_msg(log, MSGL_V, "Built with NDEBUG.\n");
+        #endif
     }
 }