[Bug c++/105631] New: GCC internal compiler error: Segmentation fault when trying to compile Qt 6.3

["ioan.mitiu at zimperium dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105631

            Bug ID: 105631
           Summary: GCC internal compiler error: Segmentation fault when
                    trying to compile Qt 6.3
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ioan.mitiu at zimperium dot com
  Target Milestone: ---

Got following error when tried to compile sources after a migration from Qt
5.12.12 -> Qt 6.3:

==================================================================
/opt/qt/qt-6.3.0/include/QtCore/qfuture_impl.h:137:34: internal compiler error:
Segmentation fault
  137 |         std::is_class_v<class T::QPrivateSignal>
      |                                  ^~~~~~~~~~~~~~
0xe4c988 internal_error(char const*, ...)
        ???:0
0x9ecbcd class_decl_loc_t::add(cp_parser*, unsigned int, tag_types, tree_node*,
bool, bool)
        ???:0
0x14e7873 c_parse_file()
        ???:0
0x14c9d9e c_common_parse_file()
        ???:0
=================================================================

In order to reproduce it is needed only to have following includes:
#include <QtWidgets>
#include <QtConcurrent>

together with a member variable like:

QFutureWatcher<std::optional<StringVector>> targetsResultWatcher;