guix: More thoroughly control native toolchain

depends/patches/qt/qtbase-moc-ignore-gcc-macro.patch

@@ -0,0 +1,17 @@
+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/qtbase/src/tools/moc/main.cpp b/qtbase/src/tools/moc/main.cpp
+--- a/qtbase/src/tools/moc/main.cpp
++++ b/qtbase/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;