Fix publishing of compressed bitmap

Before this commit we were doing changes on the published data which is problematic for multithreaded environments. We ensure the bitmap is fully processed before publishing it so that we can rely on the data dependency memory ordering constraint for correctness.

Author: BrzVlad

src/mono/mono/metadata/class-setup-vtable.c

@@ -346,10 +346,12 @@ mono_class_setup_interface_offsets_internal (MonoClass *klass, int cur_slot, int
 		}
 		if (!klass->interface_bitmap) {
 #ifdef COMPRESSED_INTERFACE_BITMAP
-			int i = mono_compress_bitmap (NULL, bitmap, bsize);
-			klass->interface_bitmap = mono_class_alloc0 (klass, i);
-			mono_compress_bitmap (klass->interface_bitmap, bitmap, bsize);
+			int len = mono_compress_bitmap (NULL, bitmap, bsize);
+			uint8_t *compressed_bitmap = mono_class_alloc0 (klass, len);
+			mono_compress_bitmap (compressed_bitmap, bitmap, bsize);
 			g_free (bitmap);
+
+			klass->interface_bitmap = compressed_bitmap;
 #else
 			klass->interface_bitmap = bitmap;
 #endif