cbc: Only check for symlink invocation if argv[0] starts with 'cbc'

libtool generates an 'lt-cbc' which the code erroneously thinks is a
symlink invocation like 'cbc-version' or 'cbc-cat'

Change-Id: I0e32a5fc2ace41506beb62c98d11db64b48fdb9b
Reviewed-on: http://review.couchbase.org/39318
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>