POT-Creation-Date line not making it into the output of gettext ("")?

[Zack Weinberg]

Lately, whenever I run the test suite locally, intl/tst-gettext fails
due to the output of gettext ("") not being as expected: the
POT-Creation-Date line is missing.  This doesn't happen with the same
patch tested using build-may-glibcs, so I'm pretty sure it's an
environment problem of some sort.  Does anyone have any idea what
might be the issue?

Example of the problem (I created tst-gettext.got and tst-gettext.exp
by hand from tst-gettext.out):

$ diff -u8 intl/tst-gettext.{got,exp}
--- intl/tst-gettext.got    2018-02-07 09:56:47.394818710 -0500
+++ intl/tst-gettext.exp    2018-02-07 09:56:48.398808299 -0500
@@ -1,11 +1,12 @@
 # test `gettext' with LANGUAGE set
 # gettext ("") failed
 Project-Id-Version: GNU libc 2.26.9000
+POT-Creation-Date: 2018-01-10 15:00+0000
 PO-Revision-Date: 2018-01-10 21:17+0100
 Last-Translator: Jochen Hein <jochen@jochen.org>
 Language-Team: German <translation-team-de@lists.sourceforge.net>
 Language: de
 MIME-Version: 1.0
 Content-Type: text/plain; charset=UTF-8
 Content-Transfer-Encoding: 8bit
 X-Bugs: Report translation errors to the Language-Team address.

zw