MB-7849:  add 'clean-grommit' target to remove directories named:
ctypes*  curl*  google-perftools*  gperftools*  libevent*  sqlite*

Change-Id: Iad31d23cb1e7c06f24b3ababc461682e854c729f
Reviewed-on: http://review.couchbase.org/26317
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>