[BlackBerry] PlatformBlackBerry.cmake: create thin AR archives
https://bugs.webkit.org/show_bug.cgi?id=110580

Patch by Xan Lopez <xlopez@igalia.com> on 2013-03-11
Reviewed by Rob Buis.

Otherwise libwebcore.a goes beyond the 4Gb file size limit and the
link phase fails.

* PlatformBlackBerry.cmake:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145372 268f45cc-cd09-0410-ab3c-d52691b4dbfc