ls-files: die instead of fprintf/exit in -i error

When ls-files was called with -i but no exclude pattern, it was
calling fprintf(stderr, "...", NULL) and then exiting.  On Solaris,
passing NULL into fprintf was causing a segfault.  On glibc systems,
it was simply producing incorrect output (eg: "(null)": ...).  The
NULL pointer was a result of argv[0] not being preserved by the option
parser.  Instead of requesting that the option parser preserve
argv[0], use die() with a constant string.

A trigger for this bug was: `git ls-files -i`

Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Ben Walton

builtin-ls-files.c

@@ -524,11 +524,8 @@ int cmd_ls_files(int argc, const char **argv, const char *prefix)
 		ps_matched = xcalloc(1, num);
 	}
 
-	if ((dir.flags & DIR_SHOW_IGNORED) && !exc_given) {
-		fprintf(stderr, "%s: --ignored needs some exclude pattern\n",
-			argv[0]);
-		exit(1);
-	}
+	if ((dir.flags & DIR_SHOW_IGNORED) && !exc_given)
+		die("ls-files --ignored needs some exclude pattern");
 
 	/* With no flags, we default to showing the cached files */
 	if (!(show_stage | show_deleted | show_others | show_unmerged |