Mark functions not returning as sudo_noreturn

We also put NOTREACHED where it applies.

plugins/sudoers/visudo.c

@@ -197,7 +197,7 @@ main(int argc, char *argv[])
 		break;
 	    case 'h':
 		help();
-		break;
+	    /* NOTREACHED */
 	    case 'I':
 		edit_includes = false;
 		break;