[Bug c++/93295] ICE in alias_ctad_tweaks

[ensadc at mailnesia dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93295

--- Comment #3 from ensadc at mailnesia dot com ---
It appears that alias_ctad_tweaks assumes the deduction of the right hand side
of the deduction guide from the alias template does not fail.

> int err = unify (ftparms, targs, ret, utype, UNIFY_ALLOW_NONE, false);
> gcc_assert (!err);

But this can fail if the RHS of the deduction guide contains `T*` or the like.

I guess this is exactly where the simplification mentioned in r278786 fails to
work.