Revised to prevent undefined macro errors with older pkg-config.

Change-Id: Ia588525e5537d7cf758b5351c0a4c5f48b28a200
Reviewed-on: https://gerrit.libreoffice.org/21595Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>