markused: fix compilation of gg programs with -skip-unused, add test to prevent regressions (#15821)

cmd/tools/vtest-all.v

@@ -169,6 +169,11 @@ fn get_all_commands() []Command {
 			okmsg: 'V compiles hello_world.v on the JS backend, with -skip-unused'
 			rmfile: 'hw_skip_unused.js'
 		}
+		res << Command{
+			line: '$vexe -skip-unused examples/2048'
+			okmsg: 'V can compile 2048 with -skip-unused.'
+			rmfile: 'examples/2048/2048'
+		}
 	}
 	res << Command{
 		line: '$vexe -o vtmp cmd/v'

cmd/tools/vtest-self.v

@@ -155,6 +155,7 @@ const (
 	skip_on_musl                  = [
 		'vlib/v/tests/profile/profile_test.v',
 		'vlib/gg/draw_fns_api_test.v',
+		'vlib/v/tests/skip_unused/gg_code.vv',
 	]
 	skip_on_ubuntu_musl           = [
 		//'vlib/v/gen/js/jsgen_test.v',