Properly export all lua-facing functions and use those for initialization (love.cpp no longer explicitly mentions implementations)

src/modules/sound/wrap_SoundData.h

@@ -37,7 +37,7 @@ namespace sound
 	int w_getSampleRate(lua_State * L);
 	int w_setSample(lua_State * L);
 	int w_getSample(lua_State * L);
-	int luaopen_sounddata(lua_State * L);
+	extern "C" int luaopen_sounddata(lua_State * L);
 
 } // sound
 } // love