[Bug c++/89224] [11/12/13/14 Regression] subscript of const vector has the wrong type

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89224

--- Comment #15 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #14)
> Causes a few regressions though:
> FAIL: g++.dg/cpp0x/constexpr-53094-1.C  -std=c++14 (internal compiler error:
> in cxx_eval_array_reference, at cp/constexpr.cc:4458)

But the fix is simple, instead of just comparing the type itself, need to
compare TYPE_MAIN_VARIANT of those types.