[Bug c++/111633] New: __restrict on a member function is permitted in an inconsistent location relative to ref-qualifiers

["richard-gccbugzilla at metafoo dot co.uk" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111633

            Bug ID: 111633
           Summary: __restrict on a member function is permitted in an
                    inconsistent location relative to ref-qualifiers
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richard-gccbugzilla at metafoo dot co.uk
  Target Milestone: ---

GCC permits __restrict-qualified member functions. When combined with
ref-qualifiers, the __restrict is written with the cv-qualifiers instead of
after the ref-qualifier:

struct A {
  // accepted
  void f() const __restrict &;
  // rejected
  void f() const & __restrict;
};

This seems backwards to me. The `*this` parameter is of type `const &__restrict
self`, so the latter syntax seems more appropriate.

Perhaps it would make sense to accept the latter syntax, and possibly deprecate
the former? (In the case of no ref-qualifier, it might make sense to also
deprecate the case where the restrict qualifier is before or interleaved with
cv-qualifiers.)