Use cast operators in headers to avoid warnings

This avoids compiler warnings when consuming the
headers from C++.

include/SDL3/SDL_events.h

@@ -1069,7 +1069,7 @@ typedef union SDL_Event
 } SDL_Event;
 
 /* Make sure we haven't broken binary compatibility */
-SDL_COMPILE_TIME_ASSERT(SDL_Event, sizeof(SDL_Event) == sizeof(((SDL_Event *)NULL)->padding));
+SDL_COMPILE_TIME_ASSERT(SDL_Event, sizeof(SDL_Event) == sizeof((SDL_static_cast(SDL_Event *, NULL))->padding));
 
 
 /* Function prototypes */