Disable -Werror=implicit-fallthrough on GCC7 and later.  Taken from upstream:
https://github.com/Tencent/rapidjson/commit/fe19b7b6016d446722621fb407738209d1a911e8
https://github.com/Tencent/rapidjson/commit/cba45fe9de6923b858edb0780e257b7257aa4f7b

diff --git a/include/rapidjson/internal/regex.h b/include/rapidjson/internal/regex.h
index 422a5240..d4039716 100644
--- a/include/rapidjson/internal/regex.h
+++ b/include/rapidjson/internal/regex.h
@@ -29,6 +29,9 @@ RAPIDJSON_DIAG_OFF(implicit-fallthrough)
 #ifdef __GNUC__
 RAPIDJSON_DIAG_PUSH
 RAPIDJSON_DIAG_OFF(effc++)
+#if __GNUC__ >= 7
+RAPIDJSON_DIAG_OFF(implicit-fallthrough)
+#endif
 #endif
 
 #ifdef _MSC_VER
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<div class='path'>path: <a href='/guix/log/?id=e18af936ff85442a841886c9434f862fb595a8b2'>root</a>/<a href='/guix/log/gnu?id=e18af936ff85442a841886c9434f862fb595a8b2'>gnu</a>/<a href='/guix/log/gnu/services?id=e18af936ff85442a841886c9434f862fb595a8b2'>services</a>/<a href='/guix/log/gnu/services/sound.scm?id=e18af936ff85442a841886c9434f862fb595a8b2'>sound.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/services/sound.scm?id=e18af936ff85442a841886c9434f862fb595a8b2&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-03-07 11:39:50 +0100'>2023-03-07</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=8390b47c045efca88785b5ed9210cb7aa13cb63a'>services: ladspa: Export accessors.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/service/sound.scm: Export ladspa-configuration? and
ladspa-configuration-plugins.
(&lt;ladspa-configuration&gt;)[plugins]: Rename accessor to ladspa-configuration-plugins.
(ladspa-environment): Adjust to use renamed plugin accessor.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Bruno Victal</td></tr>
<tr><td><span title='2023-03-07 11:39:49 +0100'>2023-03-07</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=16a48d94bc67afbfbe83ac4b2245ba94fd5bda70'>services: alsa: Export accessors.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sound.scm: Export alsa-configuration?,
alsa-configuration-alsa-plugins, alsa-configuration-pulseaudio?
and alsa-configuration-extra-options.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Bruno Victal</td></tr>
<tr><td><span title='2023-03-07 11:39:49 +0100'>2023-03-07</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=25638729cb3a0c93d5fd10af19aa1a6e76b425bd'>services: pulseaudio: Export accessors.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sound.scm: Export pulseaudio-configuration?,
pulseaudio-configuration-client-conf, pulseaudio-configuration-daemon-conf,
pulseaudio-configuration-script-file, pulseaudio-configuration-extra-script-files
and pulseaudio-configuration-system-script-file.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Bruno Victal</td></tr>
<tr><td><span title='2022-12-28 16:58:03 -0500'>2022-12-28</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=4ca649e978f08335fcabdcef693a7049082b5373'>services: pulseaudio: Fix /etc/pulse/default.pa not being used.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://issues.guix.gnu.org/60383&gt;.

* gnu/services/sound.scm (pulseaudio-etc): Produce daemon.conf
unconditionally, with the correct default-script-file location.  Produce
client.conf unconditionally.

Reported-by: Bruno Victal &lt;mirai@makinata.eu&gt;
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-02-26 09:03:01 -0500'>2022-02-26</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=e680c4086178c03eea58c1e987ea2216653dbd6a'>services: pulseaudio: Deploy the configuration files to /etc/pulse.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sound.scm (pulseaudio-environment)
[PULSE_CONFIG, PULSE_CLIENTCONFIG]: Use fixed locations, and move logic to...
(pulseaudio-etc): ... this service extension.  Guard against producing empty
files.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-02-26 09:03:01 -0500'>2022-02-26</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=60cb647a2807c4ff1ec3eeae589bb985fe7bde28'>services: pulseaudio: Add an extra-script-files configuration field.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sound.scm (&lt;pulseaudio-configuration&gt;)
[extra-script-files]: Add field.
(extra-script-files-&gt;file-union): New procedure.
(append-include-directive): Likewise.
(pulseaudio-etc): Use them.
* doc/guix.texi: Document the new 'extra-script-files- configuration field.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-02-26 09:03:01 -0500'>2022-02-26</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=1cc9060ca3db1fadcf0f2c8118529a721288f693'>services/sound: Normalize pulseaudio-configuration accessor names.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sound.scm (&lt;pulseaudio-configuration&gt;): Adjust getter names to
match convention.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-02-01 21:48:01 -0500'>2022-02-01</span></td><td><a href='/guix/commit/gnu/services/sound.scm?id=fff4daa5c2bfbf42c7ad2519f500bd254ce880a8'>services/sound: Add a udev extension for the pulseaudio service type.</a><span class='msg-avail'>...<span class='msg-tooltip'>PulseAudio provides udev rules used to adjust the configuration of certain
hardware (e.g., sound cards); ensure they get used.

* gnu/services/sound.scm (pulseaudio-service-type): Extend the
udev-service-type with the pulseaudio package.
</span></span></td><td>Maxim Cournoyer</td></tr>