LibMain: Print serenity_main() errors to the debug log

And let's make them red too, to help us notice them. :^)

Userland/Libraries/LibMain/Main.cpp

@@ -25,6 +25,7 @@ int main(int argc, char** argv)
     if (result.is_error()) {
         auto error = result.release_error();
         warnln("Runtime error: {}", error);
+        dbgln("\033[31;1mExiting with runtime error\033[0m: {}", error);
         return 1;
     }
     return result.value();