JSCBC-148: Added an arm configuration header to allow builds on ARM devices.

Change-Id: I089b7c6463bcc140c00a59ecfd2aaec5dcb06888
Reviewed-on: http://review.couchbase.org/41676
Tested-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>