ports/188320: devel/boehm-gc: update to 7.4

[amdmi3 at FreeBSD.org]

Synopsis: devel/boehm-gc: update to 7.4

Responsible-Changed-From-To: freebsd-ports-bugs->amdmi3
Responsible-Changed-By: amdmi3
Responsible-Changed-When: Wed Apr 23 15:59:34 UTC 2014
Responsible-Changed-Why: 
I'll take it.

http://www.freebsd.org/cgi/query-pr.cgi?pr=188320