editors/emacs@nox, editors/emacs-devel@nox: Fix configure error

When liblockfile is installed, configure fails, but only for the @nox
flavors.

There is an emacs-devel@gnu.org mailing list thread discussing the issue.
https://lists.gnu.org/archive/html/emacs-devel/2018-02/msg00515.html

PR: 225902
Submitted by: Yasuhiro KIMURA <yasu@utahime.org>