Copied from Debian.

From: Jérémy Bobbio <lunar@debian.org>
Subject: Remove build date
Bug-Debian: http://bugs.debian.org/782851
 In order to make unzip build reproducibly, we remove the
 (already optional) build date from the binary.

--- a/unix/unix.c
+++ b/unix/unix.c
@@ -1705,7 +1705,7 @@
 #endif /* Sun */
 #endif /* SGI */
 
-#ifdef __DATE__
+#if 0
       " on ", __DATE__
 #else
       "", ""
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<div class='path'>path: <a href='/guix/log/?id=d4732deb4f885152e98b64a70806fbe5e4b44843'>root</a>/<a href='/guix/log/etc?id=d4732deb4f885152e98b64a70806fbe5e4b44843'>etc</a>/<a href='/guix/log/etc/system-tests.scm?id=d4732deb4f885152e98b64a70806fbe5e4b44843'>system-tests.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/etc/system-tests.scm?id=d4732deb4f885152e98b64a70806fbe5e4b44843&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-03-23 00:06:58 +0100'>2020-03-23</span></td><td><a href='/guix/commit/etc/system-tests.scm?id=8b18f5cb309f670b08ad35df6425f4e9e19d8a82'>tests: Use the same source as ci.guix.gnu.org.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-05 16:33:38 +0100'>2020-03-05</span></td><td><a href='/guix/commit/etc/system-tests.scm?id=5ec4156bbcaec8337f78411204d59e59e706103b'>tests: Add a manifest for system tests.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>