Merge #5152

5152: Minor clang-tidy fix with -DWEBSOCKETS=ON -DUPNP=ON r=heinrich5991 a=def-

<!-- What is the motivation for the changes of this pull request -->

## Checklist

- [ ] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test if it works standalone, system.c especially
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: Dennis Felsing <dennis@felsin9.de>

src/engine/server/upnp.cpp

@@ -70,4 +70,4 @@ void CUPnP::Shutdown()
 	}
 }
 
-#endif
+#endif

src/engine/shared/websockets.cpp

@@ -1,7 +1,7 @@
 #if defined(CONF_WEBSOCKETS)
 
+#include <cstdlib>
 #include <map>
-#include <stdlib.h>
 #include <string>
 
 #include "base/system.h"