Avoid using memcpy() to copy structs

We can just use a regular assignment instead. This is more
type-safe since there is no need to provide the struct size.

The remaining memcpy() calls perform array copies or copies from
void pointers (which may be unaligned).

render/allocator/shm.c

@@ -31,7 +31,7 @@ static void buffer_destroy(struct wlr_buffer *wlr_buffer) {
 static bool buffer_get_shm(struct wlr_buffer *wlr_buffer,
 		struct wlr_shm_attributes *shm) {
 	struct wlr_shm_buffer *buffer = shm_buffer_from_buffer(wlr_buffer);
-	memcpy(shm, &buffer->shm, sizeof(*shm));
+	*shm = buffer->shm;
 	return true;
 }