Re-enable `copy[_nonoverlapping]()` runtime checks

This commit re-enables the debug checks for valid usages of the two
functions `copy()` and `copy_nonoverlapping()`. Those checks were com-
mented out in #79684 in order to make the functions const. All that's
been left was a FIXME, that could not be resolved until there is was way
to only do the checks at runtime.
Since #89247 there is such a way: `const_eval_select()`. This commit
uses that new intrinsic in order to either do nothing (at compile time)
or to do the old checks (at runtime).

The change itself is rather small: in order to make the checks usable
with `const_eval_select`, they are moved into a local function (one for
`copy` and one for `copy_nonoverlapping` to keep symmetry).

The change does not break referential transparency, as there is nothing
you can do at compile time, which you cannot do on runtime without get-
ting undefined behavior. The CTFE-engine won't allow missuses. The other
way round is also fine.

0 files changed, 0 insertions, 0 deletions