Remove prototypes with empty declarations (#12020)

Technically declaring a prototype with an empty declaration has been deprecated since the early days of C, but we never got a warning for it. C2x will apparently be introducing a breaking change if you are using this type of declarator, so Clang 15 has started issuing a warning with -pedantic. Although not apparently a problem for any of the compiler we build on, if feels like the right thing is to properly adhere to the C standard and use (void).

src/function_lua.c

@@ -420,7 +420,7 @@ static int luaRegisterFunction(lua_State *lua) {
 }
 
 /* Initialize Lua engine, should be called once on start. */
-int luaEngineInitEngine() {
+int luaEngineInitEngine(void) {
     luaEngineCtx *lua_engine_ctx = zmalloc(sizeof(*lua_engine_ctx));
     lua_engine_ctx->lua = lua_open();