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;
' selected='selected'>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=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>refs</a><a class='active' href='/guix/log/etc/substitutes/ci.guix.info.pub'>log</a><a href='/guix/tree/etc/substitutes/ci.guix.info.pub?id=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>tree</a><a href='/guix/commit/etc/substitutes/ci.guix.info.pub?id=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>commit</a><a href='/guix/diff/etc/substitutes/ci.guix.info.pub?id=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/etc/substitutes/ci.guix.info.pub'>
<input type='hidden' name='id' value='c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'/><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=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>root</a>/<a href='/guix/log/etc?id=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>etc</a>/<a href='/guix/log/etc/substitutes?id=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>substitutes</a>/<a href='/guix/log/etc/substitutes/ci.guix.info.pub?id=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e'>ci.guix.info.pub</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/substitutes/ci.guix.info.pub?id=c3cf0a19d78beab5f6c737015d8e50d659d3ca2e&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-07-10 00:11:00 +0200'>2020-07-10</span></td><td><a href='/guix/commit/etc/substitutes/ci.guix.info.pub?id=d283bb960f927dd5f7bb8b96bc697221e4e8ad39'>maint: Remove traces of "berlin.guixsd.org".</a><span class='msg-avail'>...<span class='msg-tooltip'>The guixsd.org domain is no longer advertised since before in 1.0.0
release in May 2019.

* etc/substitutes/berlin.guixsd.org.pub: Rename to...
* etc/substitutes/berlin.guix.gnu.org.pub: ... this.
* etc/substitutes/ci.guix.gnu.org.pub,
etc/substitutes/ci.guix.info.pub: Adjust accordingly.
* gnu/services/base.scm (%default-authorized-guix-keys): Likewise.
* guix/build/download-nar.scm (urls-for-item): Likewise.
* guix/self.scm (miscellaneous-files): Likewise.
* Makefile.am (dist_pkgdata_DATA): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-12-04 10:57:56 +0100'>2018-12-04</span></td><td><a href='/guix/commit/etc/substitutes/ci.guix.info.pub?id=6a837b6062ab405f6ca6d9c0163836769098d89b'>etc: Add "ci.guix.info.pub" public key file.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/substitutes/ci.guix.info.pub: New file.
* Makefile.am (dist_pkgdata_DATA): Add it.
* guix/self.scm (miscellaneous-files): Add
"share/guix/ci.guix.info.pub".
</span></span></td><td>Ludovic Courtès</td></tr>