Functions which return function pointers now return SDL_FunctionPointer instead of void*

This fixes the clang warning "Cast between pointer-to-function and pointer-to-object is an extension"

You can define SDL_FUNCTION_POINTER_IS_VOID_POINTER in your project to restore the previous behavior.

Fixes https://github.com/libsdl-org/SDL/issues/2866

include/SDL3/SDL_stdinc.h

@@ -738,6 +738,13 @@ SDL_FORCE_INLINE int SDL_size_add_overflow_builtin (size_t a,
 #define SDL_size_add_overflow(a, b, ret) (SDL_size_add_overflow_builtin(a, b, ret))
 #endif
 
+/* This is a generic function pointer which should be cast to the type you expect */
+#ifdef SDL_FUNCTION_POINTER_IS_VOID_POINTER
+typedef void *SDL_FunctionPointer;
+#else
+typedef void (*SDL_FunctionPointer)(void);
+#endif
+
 /* Ends C function definitions when using C++ */
 #ifdef __cplusplus
 }