Taken from: https://gitweb.gentoo.org/repo/gentoo.git/tree/x11-libs/agg/files/agg-2.5-gcc8.patch.

diff -uprN agg-2.5/include/agg_renderer_outline_aa.h agg-2.5-fixed/include/agg_renderer_outline_aa.h
--- agg-2.5/include/agg_renderer_outline_aa.h	2018-08-25 02:02:52.507254241 +0800
+++ agg-2.5-fixed/include/agg_renderer_outline_aa.h	2018-08-25 02:04:15.291175316 +0800
@@ -1375,7 +1375,7 @@ namespace agg
         //---------------------------------------------------------------------
         void profile(const line_profile_aa& prof) { m_profile = &prof; }
         const line_profile_aa& profile() const { return *m_profile; }
-        line_profile_aa& profile() { return *m_profile; }
+        const line_profile_aa& profile() { return *m_profile; }
 
         //---------------------------------------------------------------------
         int subpixel_width() const { return m_profile->subpixel_width(); }
rm></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
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<div class='path'>path: <a href='/guix/log/?id=7c2013dcc9acc7dec5152e0efd8d4eb143ce31b1'>root</a>/<a href='/guix/log/etc?id=7c2013dcc9acc7dec5152e0efd8d4eb143ce31b1'>etc</a>/<a href='/guix/log/etc/guix-daemon.conf.in?id=7c2013dcc9acc7dec5152e0efd8d4eb143ce31b1'>guix-daemon.conf.in</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/guix-daemon.conf.in?id=7c2013dcc9acc7dec5152e0efd8d4eb143ce31b1&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-07-07 23:54:20 -0400'>2021-07-07</span></td><td><a href='/guix/commit/etc/guix-daemon.conf.in?id=4cbe0127a668cbcc64087c5d311308b59d39b104'>guix-install.sh: Prompt for configuring substitutes discovery.</a><span class='msg-avail'>...<span class='msg-tooltip'>Also ensure prompt_yes_no always print the message with a trailing space,
which is more pleasing to the eye.

* etc/guix-daemon.conf.in &lt;--discover=no&gt;: New guix-daemon option.
* etc/guix-daemon.service.in: Likewise.
* etc/init.d/guix-daemon.in: Likewise.
* etc/openrc/guix-daemon.in: Likewise.
* etc/guix-install.sh (configure_substitute_discovery): New procedure.
(sys_enable_guix_daemon): Ask the user whether automatic substitute discovery
should be enabled.  Set the '--discover' argument accordingly.
(prompt_yes_no): Add a trailing space to the message.
(sys_authorize_build_farms): Remove trailing space from the message argument.
* NEWS (Distribution): Add news.
</span></span></td><td>Maxim Cournoyer</td></tr>