Submitted upstream at https://github.com/Swordfish90/cool-retro-term/issues/692

--- a/qmltermwidget/lib/TerminalCharacterDecoder.cpp	1969-12-31 18:00:01.000000000 -0600
+++ b/qmltermwidget/lib/TerminalCharacterDecoder.cpp	2021-12-27 22:07:04.452256118 -0600
@@ -19,6 +19,8 @@
     02110-1301  USA.
 */
 
+#include <cwctype>
+
 // Own
 #include "TerminalCharacterDecoder.h"
 
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<tr><td><span title='2021-05-20 01:58:04 +0200'>2021-05-20</span></td><td><a href='/guix/commit/README?id=c0087d33705f53cc3619a1a43a33602aaecc3a8b'>The #guix channel is hosted by Libera Chat.</a><span class='msg-avail'>...<span class='msg-tooltip'>* README (Contact): Update network name.
* ROADMAP: Likewise.
* doc/contributing.texi (Contributing): Likewise.
* doc/guix.texi (After System Installation): Likewise.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-10-23 12:57:20 -0400'>2020-10-23</span></td><td><a href='/guix/commit/README?id=b5aaa3a4fb985d21e21e2a67f48b52f13ebd4728'>doc: Update README.</a><span class='msg-avail'>...<span class='msg-tooltip'>* README (Installation): Do not mention installing Guix from Git anymore.
(Building from Git): Add section.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-10-22 22:47:54 -0400'>2020-10-22</span></td><td><a href='/guix/commit/README?id=503d2bfde08f9bf97bbf430516d2f19faedd4319'>README: Refer to the manual for building from Git.</a><span class='msg-avail'>...<span class='msg-tooltip'>* README (Installing Guix from Guix): Remove section.
(Installation): For installing from Git, refer to the "Building from Git"
section of the manual and suggest using './pre-inst-env guix pull' rather than
'make install' for installing Guix.
</span></span></td><td>Maxim Cournoyer</td></tr>