Fix build problems in commit aa65de042f5828968f2f6cd65f45c543a40cc3e6.

Robert Haas <rhaas@postgresql.org>

Commit: 2ccc4e972eb85829a8fe8d39fc5ce4d770ac2e2e
Author: Robert Haas <rhaas@postgresql.org>
Date: 2015-09-11T18:56:17Z
Releases: 9.6.0
Fix build problems in commit aa65de042f5828968f2f6cd65f45c543a40cc3e6.

The previous way didn't work for vpath builds, and make distprep was
busted too.

Reported off-list by Andres Freund.

Files