Correct spelling mistakes.

code/tools/lcc/etc/lcc.c

@@ -636,7 +636,7 @@ static void opt(char *arg) {
 					clist = append(&arg[3], clist);
 					return;
 				}
-				break; /* and fall thru */
+				break; /* and fall through */
 			case 'a':
 				alist = append(&arg[3], alist);
 				return;