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;
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<tr><td><span title='2023-02-09 01:07:47 +0100'>2023-02-09</span></td><td><a href='/guix/commit/gnu/tests/ganeti.scm?id=802ea1f3a43e5fb8d0b8bd2882954d8a6e49cde6'>system: Deprecate hosts-file.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system.scm (operating-system-hosts-file): Deprecate procedure.
(warn-hosts-file-field-deprecation): New procedure, helper for
deprecated variable.
(operating-system)[hosts-file]: Use helper to warn deprecated field.
(local-host-aliases): Mark as deprecated.
(local-host-entries): New procedure.
(operating-system-default-essential-services,
hurd-default-essential-services): Use hosts-service-type.  Use
'%operating-system-hosts-file' and 'local-host-entries'.
(default-/etc/hosts): Remove procedure.
(operating-system-etc-service): Remove hosts file.
* doc/guix.texi (operating-system Reference)
(Networking Services) (Virtualization Services): Rewrite documentation
entries to use hosts-service-type.

Co-authored-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Bruno Victal</td></tr>
<tr><td><span title='2021-12-13 11:49:15 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/tests/ganeti.scm?id=1052ae5f03de931b52c7a638c8e4f8d8d7093af3'>Merge branch 'master' into core-updates-frozen</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-12-12 23:20:50 +0100'>2021-12-12</span></td><td><a href='/guix/commit/gnu/tests/ganeti.scm?id=f73ba627abd46018da7f6f41ebd5efb99412cc54'>tests: Replace uses of deprecated 'static-networking-service'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/tests/ganeti.scm (%ganeti-os): Replace call to
'static-networking-service' by instantiating
STATIC-NETWORKING-SERVICE-TYPE.
* gnu/tests/networking.scm (%test-static-networking)
(%openvswitch-os, %dhcpd-os): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>