kbuild: add support for reading stdin with gen_init_cpio

Treat an argument of "-" as meaning "read stdin for cpio files" so
gen_init_cpio can be piped into.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Author: vapier

usr/gen_init_cpio.c

@@ -498,7 +498,9 @@ int main (int argc, char *argv[])
 		exit(1);
 	}
 
-	if (! (cpio_list = fopen(argv[1], "r"))) {
+	if (!strcmp(argv[1], "-"))
+		cpio_list = stdin;
+	else if (! (cpio_list = fopen(argv[1], "r"))) {
 		fprintf(stderr, "ERROR: unable to open '%s': %s\n\n",
 			argv[1], strerror(errno));
 		usage(argv[0]);