Remove handrolled strcmp()'s

Favor readability over bare-metal.

sort.c

@@ -301,7 +301,7 @@ main(int argc, char *argv[])
 			getlines(stdin, &linebuf);
 		}
 	} else for (; *argv; argc--, argv++) {
-		if ((*argv)[0] == '-' && !(*argv)[1]) {
+		if (!strcmp(*argv, "-")) {
 			*argv = "<stdin>";
 			fp = stdin;
 		} else if (!(fp = fopen(*argv, "r"))) {