Disable building of indexer for Solaris

Forestdb don't support Solaris at this time

Change-Id: I98f2b71303ed66b9a74297126b2e833126fb838a
Reviewed-on: http://review.couchbase.org/43617
Tested-by: buildbot <build@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>