empty struct is a GNU extension, patch by Carlo Bramini

git-svn-id: https://svn.code.sf.net/p/vice-emu/code/trunk@45873 379a1393-f5fb-40a0-bcee-ef074d9b53f7

Author: mrdudz

vice/src/sid/sid.c

@@ -110,7 +110,12 @@ sid_engine_t fakesid_hooks =
     fakesid_resid_state_write
 };
 
-struct sound_s {};
+struct sound_s {
+/* empty struct is a GNU extension, so add a dummy for non GNU compilers */
+#ifndef __GNUC__
+    uint8_t dummy;
+#endif
+};
 
 /* ------------------------------------------------------------------------- */