The moc executable loops through headers on CPLUS_INCLUDE_PATH and stumbles
on the GCC internal _GLIBCXX_VISIBILITY macro.  Tell it to ignore it as it is
not supposed to be looking there to begin with.

Upstream report: https://bugreports.qt.io/browse/QTBUG-83160

diff --git a/src/tools/moc/main.cpp b/src/tools/moc/main.cpp
--- a/src/tools/moc/main.cpp
+++ b/src/tools/moc/main.cpp
@@ -188,6 +188,7 @@ int runMoc(int argc, char **argv)
     dummyVariadicFunctionMacro.arguments += Symbol(0, PP_IDENTIFIER, "__VA_ARGS__");
     pp.macros["__attribute__"] = dummyVariadicFunctionMacro;
     pp.macros["__declspec"] = dummyVariadicFunctionMacro;
+    pp.macros["_GLIBCXX_VISIBILITY"] = dummyVariadicFunctionMacro;
 
     QString filename;
     QString output;
'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>refs</a><a class='active' href='/guix/log/gnu/services/avahi.scm'>log</a><a href='/guix/tree/gnu/services/avahi.scm?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>tree</a><a href='/guix/commit/gnu/services/avahi.scm?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>commit</a><a href='/guix/diff/gnu/services/avahi.scm?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/avahi.scm'>
<input type='hidden' name='id' value='956463a4c442d08721a60f3b39cbd04b6c6588ea'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>root</a>/<a href='/guix/log/gnu?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>gnu</a>/<a href='/guix/log/gnu/services?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>services</a>/<a href='/guix/log/gnu/services/avahi.scm?id=956463a4c442d08721a60f3b39cbd04b6c6588ea'>avahi.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/avahi.scm?id=956463a4c442d08721a60f3b39cbd04b6c6588ea&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-11-18 15:44:39 +0100'>2022-11-18</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=8d9647d8a77a67013c48166561134d92b5224264'>services: Add Shepherd 'configuration' action to various services.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/avahi.scm (avahi-shepherd-service): Add 'actions' field.
* gnu/services/base.scm (nscd-actions): Add call to
'shepherd-configuration-action'.
* gnu/services/desktop.scm (upower-shepherd-service): Add 'actions'
field.
(elogind-shepherd-service): Likewise.
* gnu/services/dict.scm (dicod-shepherd-service): Likewise.
* gnu/services/networking.scm (openntpd-shepherd-service): Likewise.
(tor-shepherd-service): Likewise.
* gnu/services/ssh.scm (openssh-shepherd-service): Likewise.
* gnu/services/web.scm (nginx-shepherd-service): Likewise.
* gnu/services/xorg.scm (gdm-shepherd-service): Likewise.
* gnu/tests/base.scm (run-basic-test)["nscd configuration action"]: New
test.
* doc/guix.texi (Services): Document it.
</span></span></td><td>Ludovic Courtès</td></tr>