add comment FALLTHROUGH which recognize by many lint tools

atomicio.c

@@ -53,6 +53,7 @@ atomicio(f, fd, _s, n)
 			if (errno == EINTR || errno == EAGAIN)
 #endif
 				continue;
+			/* FALLTHROUGH */
 		case 0:
 			return (res);
 		default:

cli-runopts.c

@@ -315,6 +315,7 @@ void cli_getopts(int argc, char ** argv) {
 					break;
 				case 'b':
 					next = &dummy;
+					/* FALLTHROUGH */
 				default:
 					fprintf(stderr,
 						"WARNING: Ignoring unknown option -%c\n", c);