[PATCH] D138539: Use std::nullopt_t instead of NoneType (NFC)

[Balázs Benics via Phabricator via cfe-commits]

steakhal added a comment.

Oh, I forgot to mention why this change breaks the equality operator of `llvm::StringSet`. It's because the `StringMap::operator==` will try to compare the `value` as well, which is of type `std::nullopt_t` and that has no equality comparison operator.
Previously, the `enum class NoneType` has a default one.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D138539/new/

https://reviews.llvm.org/D138539