[Bug c++/69375] GCC allows PMF type "void (T::*)()" to be caught as "void (T::*)() const"

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69375

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For the attached reproducer this condition is never true in
cp_build_qualified_type_real

  /* But preserve any function-cv-quals on a FUNCTION_TYPE.  */
  if (TREE_CODE (type) == FUNCTION_TYPE)
    type_quals |= type_memfn_quals (type);

As far as I can tell this is what's supposed to put the cv-quals back onto the
function type, so we'd have a pointee of type void() const not void().