Allocator: Fail building when trying to MEM_delete a void pointer

`MEM_delete()` is designed for type safe destruction and freeing, void
pointers make that impossible.
Was reviewing a patch that was trying to free a C-style custom data
pointer this way. Apparently MSVC compiles this just fine, other
compilers error out. Make sure this is a build error on all platforms
with a useful message.

intern/guardedalloc/MEM_guardedalloc.h

@@ -281,6 +281,8 @@ inline T *MEM_new(const char *allocation_name, Args &&...args)
  */
 template<typename T> inline void MEM_delete(const T *ptr)
 {
+  static_assert(!std::is_void_v<T>,
+                "MEM_delete on a void pointer not possible. Cast it to a non-void type?");
   if (ptr == nullptr) {
     /* Support #ptr being null, because C++ `delete` supports that as well. */
     return;