Don't create a corefile just because we don't have tcmalloc

Change-Id: I2a01322d74033a7c80cbf82bd1cb71cb732bd031
Reviewed-on: http://review.couchbase.org/42837
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>