Replaced SDL_SIMDAlloc(), SDL_SIMDRealloc(), and SDL_SIMDFree() with SDL_aligned_alloc() and SDL_aligned_free()

Fixes https://github.com/libsdl-org/SDL/issues/5641

src/stdlib/SDL_stdlib.c

@@ -686,3 +686,40 @@ int SDL_isblank(int x)
     return ((x) == ' ') || ((x) == '\t');
 }
 #endif
+
+void *SDL_aligned_alloc(size_t alignment, size_t size)
+{
+    size_t padding;
+    Uint8 *retval = NULL;
+
+    if (alignment < sizeof(void*)) {
+        alignment = sizeof(void*);
+    }
+    padding = (alignment - (size % alignment));
+
+    if (SDL_size_add_overflow(size, alignment, &size) == 0 &&
+        SDL_size_add_overflow(size, sizeof(void *), &size) == 0 &&
+        SDL_size_add_overflow(size, padding, &size) == 0) {
+        void *original = SDL_malloc(size);
+        if (original) {
+            /* Make sure we have enough space to store the original pointer */
+            retval = (Uint8 *)original + sizeof(original);
+
+            /* Align the pointer we're going to return */
+            retval += alignment - (((size_t)retval) % alignment);
+
+            /* Store the original pointer right before the returned value */
+            SDL_memcpy(retval - sizeof(original), &original, sizeof(original));
+        }
+    }
+    return retval;
+}
+
+void SDL_aligned_free(void *mem)
+{
+    if (mem) {
+        void *original;
+        SDL_memcpy(&original, ((Uint8 *)mem - sizeof(original)), sizeof(original));
+        SDL_free(original);
+    }
+}