Don't create cc and c++ ccache links, since that compiler doesn't exist

Change-Id: I5c211868dbac19cc15d926fe5cffd3388bc09b4f
Reviewed-on: http://review.couchbase.org/40812
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>