moc mis-parses third-party headers and generates invalid code

/usr/bin/qmake6 -o Makefile ../moctest/moctest.pro -spec linux-g++ CONFIG+=debug CONFIG+=qml_debug
g++ -c -pipe -g -Wall -Wextra -fPIC -D_REENTRANT -DQT_QML_DEBUG -DQT_CORE_LIB -I../moctest -I. -I/usr/include/qt6 -I/usr/include/qt6/QtCore -I. -I/usr/lib/qt6/mkspecs/linux-g++ -o main.o ../moctest/main.cpp
In file included from ../moctest/main.cpp:14:
./main.moc:58:43: error: ‘llvm::yaml::O’ has not been declared
   58 | Q_CONSTINIT const QMetaObject llvm::yaml::O::staticMetaObject = { {
      |                                           ^
./main.moc:62:5: error: ‘qt_static_metacall’ was not declared in this scope
   62 |     qt_static_metacall,
      |     ^~~~~~~~~~~~~~~~~~
./main.moc:71:18: error: ‘llvm::yaml::O’ has not been declared
   71 | void llvm::yaml::O::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
      |                  ^
./main.moc:79:32: error: ‘llvm::yaml::O’ has not been declared
   79 | const QMetaObject *llvm::yaml::O::metaObject() const
      |                                ^
./main.moc:79:48: error: non-member function ‘const QMetaObject* metaObject()’ cannot have cv-qualifier
   79 | const QMetaObject *llvm::yaml::O::metaObject() const
      |                                                ^~~~~
./main.moc: In function ‘const QMetaObject* metaObject()’:
./main.moc:81:21: error: ‘QScopedPointer<QObjectData> QObject::d_ptr’ is protected within this context
   81 |     return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
      |                     ^~~~~
In file included from /usr/include/qt6/QtCore/QObject:1,
                 from ../moctest/main.cpp:1:
/usr/include/qt6/QtCore/qobject.h:403:33: note: declared protected here
  403 |     QScopedPointer<QObjectData> d_ptr;
      |                                 ^~~~~
./main.moc:81:21: error: invalid use of non-static data member ‘QObject::d_ptr’
   81 |     return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
      |                     ^~~~~
/usr/include/qt6/QtCore/qobject.h:403:33: note: declared here
  403 |     QScopedPointer<QObjectData> d_ptr;
      |                                 ^~~~~
./main.moc:81:50: error: ‘QScopedPointer<QObjectData> QObject::d_ptr’ is protected within this context
   81 |     return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
      |                                                  ^~~~~
/usr/include/qt6/QtCore/qobject.h:403:33: note: declared protected here
  403 |     QScopedPointer<QObjectData> d_ptr;
      |                                 ^~~~~
./main.moc:81:50: error: invalid use of non-static data member ‘QObject::d_ptr’
   81 |     return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
      |                                                  ^~~~~
/usr/include/qt6/QtCore/qobject.h:403:33: note: declared here
  403 |     QScopedPointer<QObjectData> d_ptr;
      |                                 ^~~~~
./main.moc: At global scope:
./main.moc:84:19: error: ‘llvm::yaml::O’ has not been declared
   84 | void *llvm::yaml::O::qt_metacast(const char *_clname)
      |                   ^
./main.moc: In function ‘void* qt_metacast(const char*)’:
./main.moc:88:35: error: invalid use of ‘this’ in non-member function
   88 |         return static_cast<void*>(this);
      |                                   ^~~~
./main.moc:89:32: error: cannot call member function ‘virtual void* QObject::qt_metacast(const char*)’ without object
   89 |     return QObject::qt_metacast(_clname);
      |            ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
./main.moc: At global scope:
./main.moc:92:17: error: ‘llvm::yaml::O’ has not been declared
   92 | int llvm::yaml::O::qt_metacall(QMetaObject::Call _c, int _id, void **_a)
      |                 ^
./main.moc: In function ‘int qt_metacall(QMetaObject::Call, int, void**)’:
./main.moc:94:31: error: cannot call member function ‘virtual int QObject::qt_metacall(QMetaObject::Call, int, void**)’ without object
   94 |     _id = QObject::qt_metacall(_c, _id, _a);
      |           ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
make: *** [Makefile:573: main.o] Error 1