[Bug c++/111272] [13/14 Regression] Truncated error messages with -std=c++23 and -std=c++26

[pkeir at outlook dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111272

--- Comment #4 from Paul Keir <pkeir at outlook dot com> ---
I believe P2448R2 would only allow the code, without the static_assert.
Explicitly calling `test()`, `Jam::Jam()` and then `Jam::ft()` here would mean
evaluating a non-constexpr function (i.e. `ft`). ft is *constexpr-suitable*,
but still needs the `constexpr` specifier when it is constant evaluated.