Here is a suitable ChangeLog entry:

2013-01-20  Thien-Thi Nguyen  <ttn@gnuvola.org>  (tiny change)

	Don't get fooled when running "make check" inside Emacs.

	Some versions of Emacs set the env var 'EMACS' to 't'
	for child processes.  Thus, when running from inside Emacs,
	'$(MAKE) -e' erroneously allows the 't' to override the one
	in the Makefile.  This change avoids that problem.

	* t/lisp-flags.sh: Unset var 'EMACS'.

Here is the patch, proper: