[llvm] [ADT] Implement ArrayRef::operator< and other comparisons (PR #147277)

[David Blaikie via llvm-commits]

dwblaikie wrote:

Does std::span have these operators, and if it does, are they SFINAE-safe there?  And if so, should they be made SFINAE-safe here too?

https://github.com/llvm/llvm-project/pull/147277