This following patch was originally found at the debian mingw-w64 team's
mingw-w64 repo located here:
https://salsa.debian.org/mingw-w64-team/mingw-w64.git

Invoke the following in the aforementioned repo to see the original patch:

  $ git show 9a33f50:debian/patches/reproducible-build.patch

Description: Drop __DATE__ from gendef and genlib
Author: Stephen Kitt <skitt@debian.org>

This allows gendef and genlib to be built reproducibly.

--- a/mingw-w64-tools/gendef/src/gendef.c
+++ b/mingw-w64-tools/gendef/src/gendef.c
@@ -196,7 +196,6 @@
                    "  By default, the output files are named after their DLL counterparts\n"
                    "  gendef MYDLL.DLL     Produces MYDLL.def\n"
                    "  gendef - MYDLL.DLL   Prints the exports to stdout\n");
-  fprintf (stderr, "\nBuilt on %s\n", __DATE__);
   fprintf (stderr, "\nReport bugs to <mingw-w64-public@lists.sourceforge.net>\n");
   exit (0);
 }
--- a/mingw-w64-tools/genlib/src/genlib.c
+++ b/mingw-w64-tools/genlib/src/genlib.c
@@ -123,7 +123,6 @@
 "Usage example:\n"
 "  By default, the output file is named after the DLL counterpart\n"
 "  genlib mydef.def    Produces libmydll.a\n"
-"\nBuilt on " __DATE__ "\n"
 "\nReport bugs to <martellmalone@gmail.com>\n"
 ;

c7b4636fafb772c94adb8f05961b5b39f16'>tree</a><a href='/guix/commit/gnu/packages/popt.scm?id=9744cc7b4636fafb772c94adb8f05961b5b39f16'>commit</a><a href='/guix/diff/gnu/packages/popt.scm?id=9744cc7b4636fafb772c94adb8f05961b5b39f16'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/popt.scm'>
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<div class='path'>path: <a href='/guix/log/?id=9744cc7b4636fafb772c94adb8f05961b5b39f16'>root</a>/<a href='/guix/log/gnu?id=9744cc7b4636fafb772c94adb8f05961b5b39f16'>gnu</a>/<a href='/guix/log/gnu/packages?id=9744cc7b4636fafb772c94adb8f05961b5b39f16'>packages</a>/<a href='/guix/log/gnu/packages/popt.scm?id=9744cc7b4636fafb772c94adb8f05961b5b39f16'>popt.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/gnu/packages/popt.scm?id=9744cc7b4636fafb772c94adb8f05961b5b39f16&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-01-15 20:36:32 +0100'>2020-01-15</span></td><td><a href='/guix/commit/gnu/packages/popt.scm?id=981bd6e69cc7d58889b8b14d582b5519be7f7246'>gnu: popt: Add a source file name.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/popt.scm (popt)[source](file-name): New field.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-01-15 01:13:18 +0100'>2020-01-15</span></td><td><a href='/guix/commit/gnu/packages/popt.scm?id=98ca002aaf14b38ae3445e801d497177888f8438'>gnu: popt: Reverse source mirror entries.</a><span class='msg-avail'>...<span class='msg-tooltip'>Commit 8f4cff0e21e4142d5f51022ef1efad569c3ca0bc accidentally caused rebuilds
because the expected file name changed.

* gnu/packages/popt.scm (popt)[source](uri): Add the Debian mirror last.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-01-14 23:50:23 +0100'>2020-01-14</span></td><td><a href='/guix/commit/gnu/packages/popt.scm?id=8f4cff0e21e4142d5f51022ef1efad569c3ca0bc'>gnu: popt: Update source URI.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/popt.scm (popt)[source](uri): Add Debian mirror.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-06-15 18:28:13 +0200'>2019-06-15</span></td><td><a href='/guix/commit/gnu/packages/popt.scm?id=02dad49d423146c2f86df00df2466d6616c0f6a2'>gnu: gengetopt: Update to 2.23.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/popt.scm (gengetopt): Update to 2.23.
[native-inputs]: New field.
</span></span></td><td>Ludovic Courtès</td></tr>