[Bug libstdc++/114149] lexicographical_compare should use memcmp for C++20 contiguous iterators as well as pointers

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114149

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I'm writing a proposal to say the library can assume contiguous iterators are
sane.