[libc++] ADL-proof <iterator>. `__convert_to_integral` is not a customization…

Authored by arthur.j.odwyer on Dec 7 2020, 8:42 PM.


[libc++] ADL-proof <iterator>. __convert_to_integral is not a customization point.

The interesting change here is that we no longer consider __convert_to_integral
an ADL customization point for the user's types. I think the new behavior
is defensible. The old behavior had come from D7449, where Marshall explicitly
said "people can't define their own [__convert_to_integral overloads]."

Differential Revision: https://reviews.llvm.org/D92814