real_path: set errno when max number of symlinks is exceeded

Set errno to ELOOP when the maximum number of symlinks is exceeded, as
would be done by other symlink-resolving functions.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

abspath.c

@@ -141,6 +141,8 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path,
 			strbuf_reset(&symlink);
 
 			if (num_symlinks++ > MAXSYMLINKS) {
+				errno = ELOOP;
+
 				if (die_on_error)
 					die("More than %d nested symlinks "
 					    "on path '%s'", MAXSYMLINKS, path);