Non-dependent consteval calls in template arg position are considered dependent

[gwllx]

Issue Summary

Non-dependent consteval calls in template arg position are in some cases (e.g. in a requires-clause or default template argument) considered dependent. This causes EDG to require the typename keyword where the other compilers/standard do not. Such cases may lead to unsatisfied constraints or unexpected SFINAE results.

Reproducing Source Code

template <class T, class U>
struct is_same { static constexpr bool value = false; };
template <class T>
struct is_same<T, T> { static constexpr bool value = true; };
template <class T, class U>
concept same_as = is_same<T, U>::value;

template <int N> struct S;
template <> struct S<0> { using type = int; };

consteval int val() { return 0; }

template <class T>
  requires same_as<S<val()>::type, T>
int f(T p) { return p; }

https://godbolt.org/z/oaEad5Yre

The same issue is present when the call is part of a template arg within a default template arg:
https://godbolt.org/z/YTxEz438a

Command-line Options

cpfe --c++20

Type of Issue

[Front End] This code SHOULD compile with these options.

Additional Details

Suggested patch:
non_dependent_consteval_call_as_template_arg.patch

call_did_not_fold_to_constant does not account for the case where a non-dependent consteval call was made within a expr_stack->consteval_need_not_fold context and instead transforms the call operand into a template-dependent constant.

Reproducing (Standard) Configuration(s)

linux-gcc-debug

Reproducing (Non-standard) Configuration

No response

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