Make libtiff link on OS X 10.9

Undefining the 'inline' keyword doesn't look very wise nowadays, and it
did cause duplicate symbol erros at link time when linking against the
10.9 SDK.

Change-Id: Ie6f8639fb920e57289c7d0ad8952603abcfe7377
Reviewed-by: aavit <eirik.aavitsland@digia.com>