Honor SOURCE_DATE_EPOCH when exporting configuration date.
Autoconf-level patch submitted upstream on Wed Apr 13 17:03:23 UTC 2016

--- a/configure
+++ b/configure
@@ -27737,7 +28573,14 @@
 
 
 ## Configuration date
- CONFIG_DATE="`date`"
+ CONFIG_DATE="`date -u`"
+if test -n "$SOURCE_DATE_EPOCH"; then
+  CONFIG_DATE=`date -u -d "@$SOURCE_DATE_EPOCH" 2>/dev/null \
+               || date -u -r "$SOURCE_DATE_EPOCH" 2>/dev/null`
+  if test -z "$CONFIG_DATE"; then
+    as_fn_error $? "malformed SOURCE_DATE_EPOCH" "$LINENO" 5
+  fi
+fi
 
 ## User doing the configuration
  CONFIG_USER="`whoami`@`hostname`"
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<tr><td><span title='2020-08-01 09:00:44 +0200'>2020-08-01</span></td><td><a href='/guix/commit/gnu/packages/digest.scm?id=08447d3a7556fb6355a32c6d5ccb6d4768b8e12d'>gnu: Update xxhash to 0.8.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/digest.scm (xxhash): Update to 0.8.0.

Signed-off-by: Mathieu Othacehe &lt;othacehe@gnu.org&gt;
</span></span></td><td>Hendursaga</td></tr>
<tr><td><span title='2020-06-29 15:47:11 +0200'>2020-06-29</span></td><td><a href='/guix/commit/gnu/packages/digest.scm?id=1d25cfbaf4b707f5af9aafe6ac3d8828c5b89f45'>gnu: xxhash: Detect vector instructions at run time.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/digest.scm (xxhash)[arguments]: Set DISPATCH=1 make flag
on x86.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-06-29 15:47:11 +0200'>2020-06-29</span></td><td><a href='/guix/commit/gnu/packages/digest.scm?id=8db9300454d067dfa023430e51d7f394f203d849'>gnu: xxhash: Update to 0.7.4.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/digest.scm (xxhash): Update to 0.7.4.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-06-29 15:47:11 +0200'>2020-06-29</span></td><td><a href='/guix/commit/gnu/packages/digest.scm?id=9c1324a4164eb7bf3a912b185b2ab9c86447e005'>gnu: xxhash: Cross-compile.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/digest.scm (xxhash)[arguments]: Use CC-FOR-TARGET.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-03-11 21:39:16 -0400'>2020-03-11</span></td><td><a href='/guix/commit/gnu/packages/digest.scm?id=4b5a0c0540fb1008daa6834f05aa94c85803e620'>gnu: xxHash: Update to 0.7.3.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/digest.scm (xxhash): Update to 0.7.3.
</span></span></td><td>Leo Famulari</td></tr>
<tr><td><span title='2019-12-23 19:45:57 +0100'>2019-12-23</span></td><td><a href='/guix/commit/gnu/packages/digest.scm?id=491b91dc8a879e092c451ac15a9842f2feb40be4'>gnu: xxhash: Update to 0.7.2.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/digest.scm (xxhash): Update to 0.7.2.
[arguments]: Run ‘make check’ in parallel.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>