gg: enable clean compilation without notices for ./v -check-unused-fn-args examples/tetris/

Author: spytheman

vlib/gg/text_rendering.c.v

@@ -23,7 +23,7 @@ pub mut:
 
 const buff_size = int($d('gg_text_buff_size', 2048))
 
-fn clear_atlas_callback(uptr voidptr, error int, val int) {
+fn clear_atlas_callback(uptr voidptr, error int, _val int) {
 	if error == 1 { // atlas overflow error code
 		fons := unsafe { &fontstash.Context(uptr) }
 		fons.reset_atlas(buff_size, buff_size)