[Bug libstdc++/89446] [7/8 Regression] __builtin_constant_p expression crashes in char_traits::compare

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89446

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> Not just
> while (__i < __n && __builtin_constant_p(__a[__i]))
> ?

Yeah that's what I'm testing, not sure where the (i < n && __bcp && i < n)
version came from!