Always provide the same date and time in 'Py_GetBuildInfo'.
This is the information shown at the REPL and in 'sys.version'.
We cannot pass it in CPPFLAGS due to whitespace in the DATE string.

--- a/Modules/getbuildinfo.c
+++ b/Modules/getbuildinfo.c
@@ -4,6 +4,10 @@
 #include <stdio.h>
 #endif
 
+/* Deterministic date and time.  */
+#define DATE "Jan  1 1970"
+#define TIME "00:00:01"
+
 #ifndef DATE
 #ifdef __DATE__
 #define DATE __DATE__
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<tr><td><span title='2020-12-06 21:55:18 +0100'>2020-12-06</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=329fa5bdbb621dae586cbfb062cbd3b295880ba5'>Revert "linux-container: Correct test for unprivileged user namespace support."</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-12-03 16:25:45 +0000'>2020-12-03</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=8bc5ca5160db3d82bd5b6b2b7ed80c96f42bd33e'>linux-container: Correct test for unprivileged user namespace support.</a><span class='msg-avail'>...</span></td><td>Paul Garlick</td></tr>
<tr><td><span title='2020-10-01 12:51:13 +0200'>2020-10-01</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=e74818353882f187e5971b5a3a481f17df883dbe'>linux-container: Reset jailed root permissions.</a><span class='msg-avail'>...</span></td><td>Jelle Licht</td></tr>
<tr><td><span title='2020-09-10 09:38:52 +0200'>2020-09-10</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=b3a83f1ece4b6c8bfcc2a9875df51142c0e39904'>build: linux-container: Fix run-container.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-09-02 17:05:23 +0200'>2020-09-02</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=5316dfc0f125b658e4a2acf7f00f49501663d943'>linux-container: Do not jail the container unconditionally.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2019-09-12 23:07:43 +0200'>2019-09-12</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=d236cd16a7173278ca69578d3e7ce4d1ce55e04c'>linux-container: "run-container" scripts shows the container's PID.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-07-06 00:26:58 +0200'>2019-07-06</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=935e79af61f4d903e562362cdd828be807e15581'>linux-container: Mount a new /dev/pts instance in the container.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-06-23 19:53:03 +0200'>2019-06-23</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=40c369b23442ace588d8c85f62f1741c17ed65c0'>linux-container: Remove dependency on (guix utils).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-04-02 18:15:37 +0200'>2019-04-02</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=af76c020bf19de5fe2e92f31d8b85cbd55c481de'>linux-container: Make the guest UID and GID a parameter.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-01-15 23:29:33 +0100'>2018-01-15</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=95aa64bc48cae061effafa7675ea9d9ccbe311a4'>linux-container: Work around EBADF errors upon exit.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-10-11 11:12:33 +0200'>2017-10-11</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=1c65cca5743e9171bbd94307195f123d26c0535e'>file-systems: 'mount-file-system' now takes a &lt;file-system&gt; object.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-02-07 00:08:10 +0100'>2017-02-07</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=c90db25f4cf1f98f3f4f3af38d175a14ffb8c32a'>linux-container: Add 'container-excursion*'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-02-06 10:51:25 +0100'>2017-02-06</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=36c4917c910f434524aae32725582d5bc51a44e0'>linux-container: Add comment on exception handling.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-02-06 10:51:25 +0100'>2017-02-06</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=168aba297866295d96779239e9662821ce9e66ae'>linux-container: Do not rely on 'isatty?'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>