ports/156912: Fix port: mail/thunderbird occasionally breaks with gmake-3.82

[crees at FreeBSD.org]

Synopsis: Fix port: mail/thunderbird occasionally breaks with gmake-3.82

Responsible-Changed-From-To: gecko->crees
Responsible-Changed-By: crees
Responsible-Changed-When: Thu Jun 30 20:56:50 UTC 2011
Responsible-Changed-Why: 
I'll take it.

http://www.freebsd.org/cgi/query-pr.cgi?pr=156912