setup_temporary_shallow: move tempfile struct into function

The setup_temporary_shallow() function creates a temporary
file, but we never access the tempfile struct outside of the
function. This is OK, since it means we'll just clean up the
tempfile on exit.  But we can simplify the code a bit by
moving the global tempfile struct to the only function in
which it's used.

Note that it must remain "static" due to tempfile.c's
requirement that tempfile storage never goes away until
program exit.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

shallow.c

@@ -286,22 +286,21 @@ int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 	return write_shallow_commits_1(out, use_pack_protocol, extra, 0);
 }
 
-static struct tempfile temporary_shallow;
-
 const char *setup_temporary_shallow(const struct oid_array *extra)
 {
+	static struct tempfile temp;
 	struct strbuf sb = STRBUF_INIT;
 	int fd;
 
 	if (write_shallow_commits(&sb, 0, extra)) {
-		fd = xmks_tempfile(&temporary_shallow, git_path("shallow_XXXXXX"));
+		fd = xmks_tempfile(&temp, git_path("shallow_XXXXXX"));
 
 		if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 			die_errno("failed to write to %s",
-				  get_tempfile_path(&temporary_shallow));
-		close_tempfile(&temporary_shallow);
+				  get_tempfile_path(&temp));
+		close_tempfile(&temp);
 		strbuf_release(&sb);
-		return get_tempfile_path(&temporary_shallow);
+		return get_tempfile_path(&temp);
 	}
 	/*
 	 * is_repository_shallow() sees empty string as "no shallow