Search in /usr/lib64/erlang/usr/include as well

Change-Id: I4ccbfb0aa34fbddc3d66c73d7b8698feafd5951b
Reviewed-on: http://review.couchbase.org/34879
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>