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;
on>
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<div class='path'>path: <a href='/guix/log/?id=5855813f772653c2cfe03d2a7e4a209e42687e29'>root</a>/<a href='/guix/log/tests?id=5855813f772653c2cfe03d2a7e4a209e42687e29'>tests</a>/<a href='/guix/log/tests/lzlib.scm?id=5855813f772653c2cfe03d2a7e4a209e42687e29'>lzlib.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/tests/lzlib.scm?id=5855813f772653c2cfe03d2a7e4a209e42687e29&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-01-16 23:14:05 +0100'>2020-01-16</span></td><td><a href='/guix/commit/tests/lzlib.scm?id=3597c0396b9bd6440c02462107c743c6aeb29672'>lzlib: Define 'dictionary-size+match-length-limit'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/lzlib.scm (%compression-levels): Splice the rest of each element.
(dictionary-size+match-length-limit): New procedure.
(make-lzip-output-port, make-lzip-input-port/compressed): Use it.
* tests/lzlib.scm ("Bytevector of size relative to Lzip internal buffers (2 * dictionary)"):
Use 'dictionary-size+match-length-limit' instead of 'assoc-ref'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-12-01 16:51:40 +0100'>2019-12-01</span></td><td><a href='/guix/commit/tests/lzlib.scm?id=2c5dd47ceffd61d155e64dcb1764ffaea0ffd546'>tests: lzlib: Do not fail if lzlib in not available.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/lzlib.scm: Use test-assert* for all test cases, so that there are no
failures if lzlib is unavailable.
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2019-05-27 22:47:24 +0200'>2019-05-27</span></td><td><a href='/guix/commit/tests/lzlib.scm?id=2a991f3ae4823730395c7970d83159e93d5f5fe2'>lzlib: Add 'make-lzip-input-port/compressed'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/lzlib.scm (lzwrite!, make-lzip-input-port/compressed): New
procedures.
* tests/lzlib.scm ("make-lzip-input-port/compressed"): New test.
* guix/tests.scm (%seed): Export.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-05-06 23:21:33 +0200'>2019-05-06</span></td><td><a href='/guix/commit/tests/lzlib.scm?id=fea338c6ca1922097fa233be85f424c152a4f507'>Add (guix lzlib).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/lzlib.scm, tests/lzlib.scm: New files.
* Makefile.am (MODULES): Add guix/lzlib.scm.
(SCM_TESTS): Add tests/lzlib.scm.
* m4/guix.m4 (GUIX_LIBLZ_LIBDIR): New macro.
* configure.ac (LIBLZ_LIBDIR): Use it.  Define and substitute
'LIBLZ'.
* guix/config.scm.in (%liblz): New variable.
* guix/self.scm (make-config.scm): Add TODO comment.

Co-authored-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Pierre Neidhardt</td></tr>