[flang] Use std::nullopt instead of None (NFC)
authorKazu Hirata <kazu@google.com>
Sun, 4 Dec 2022 21:52:47 +0000 (13:52 -0800)
committerKazu Hirata <kazu@google.com>
Sun, 4 Dec 2022 21:52:47 +0000 (13:52 -0800)
commit8d6589cba7cde886d2e189ea84c8bb17e12da861
tree0b445e0e357848099eabebff471ef07b3228b4c7
parent552109719071677c0ff9bd03f662f6c3eb70285a
[flang] Use std::nullopt instead of None (NFC)

I've verified that every change in this patch affects generated files
and would reduce the number of warnings if None were deprecated.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716
flang/include/flang/Optimizer/Dialect/FIROps.td