Implement POSIX 2024's -mount

This reverts commit 4f80c17.

Link: https://www.austingroupbugs.net/view.php?id=1133

src/parse.c

@@ -1694,10 +1694,7 @@ static struct bfs_expr *parse_mount(struct bfs_parser *parser, int arg1, int arg
 		return NULL;
 	}
 
-	parse_expr_warning(parser, expr, "In the future, ${blu}%s${rs} will skip mount points entirely, unlike\n", expr->argv[0]);
-	bfs_warning(parser->ctx, "${blu}-xdev${rs}, due to http://austingroupbugs.net/view.php?id=1133.\n\n");
-
-	parser->ctx->flags |= BFTW_PRUNE_MOUNTS;
+	parser->ctx->flags |= BFTW_SKIP_MOUNTS;
 	parser->mount_arg = expr->argv;
 	return expr;
 }

tests/posix/L_mount.out

@@ -0,0 +1,2 @@
+.
+./foo

tests/common/mount.out → tests/posix/mount.out

@@ -1,4 +1,3 @@
 .
 ./foo
 ./foo/bar
-./mnt