It seems the www/xsp port does not configure anymore since the upgrade of the mono port to 4.0.1. You can find details here : http://pkglogs.iaelu.net/iaelunet-default/2015-05-23_16h38m06s/build.html but I'm attaching the www/xsp poudriere build log here too.
Created attachment 157083 [details] www/xsp poudriere build log
A commit references this bug: Author: antoine Date: Sat May 23 23:30:24 UTC 2015 New revision: 387192 URL: https://svnweb.freebsd.org/changeset/ports/387192 Log: - Fix configure with mono 4 - Remove redundant depends PR: 200413 Reported by: pkg-fallout Changes: head/www/xsp/Makefile