Added generated build files to .gitignore

Change-Id: I3ecd156cd3221c725af359cb6d9a59276cc2c8e7
Reviewed-on: http://review.couchbase.org/26634
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>