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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<div class='path'>path: <a href='/guix/log/?id=47d0346553fdad9795c9390a60944ccaad7e5255&amp;showmsg=1'>root</a>/<a href='/guix/log/gnu?id=47d0346553fdad9795c9390a60944ccaad7e5255&amp;showmsg=1'>gnu</a>/<a href='/guix/log/gnu/packages?id=47d0346553fdad9795c9390a60944ccaad7e5255&amp;showmsg=1'>packages</a>/<a href='/guix/log/gnu/packages/patches?id=47d0346553fdad9795c9390a60944ccaad7e5255&amp;showmsg=1'>patches</a>/<a href='/guix/log/gnu/packages/patches/libsequoia-remove-store.patch?id=47d0346553fdad9795c9390a60944ccaad7e5255&amp;showmsg=1'>libsequoia-remove-store.patch</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/packages/patches/libsequoia-remove-store.patch?id=47d0346553fdad9795c9390a60944ccaad7e5255'>Collapse</a>)</th><th class='left'>Author</th></tr>
<tr class='logheader'><td><span title='2021-12-30 21:32:44 +0100'>2021-12-30</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/patches/libsequoia-remove-store.patch?id=e0573838487a5ca00031448210d782e3737333c0'>gnu: Add libsequoia.</a></td><td>Hartmut Goebel</td></tr>
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* gnu/packages/sequoia.scm (sequoia-package-origin): New variable.
  (libsequoia): New variable.
* gnu/packages/patches/sequoia-fix-ffi-Makefile.patch,
  gnu/packages/patches/sequoia-remove-store.patch New files.
* gnu/local.mk (dist_patch_DATA): Add them.


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