[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

diff --git a/flang/include/flang/Optimizer/Dialect/FIROps.td b/flang/include/flang/Optimizer/Dialect/FIROps.td
index bf682b7..c0ea063 100644 (file)
--- a/flang/include/flang/Optimizer/Dialect/FIROps.td
+++ b/flang/include/flang/Optimizer/Dialect/FIROps.td
@@ -2090,7 +2090,7 @@ def fir_DoLoopOp : region_Op<"do_loop",
     OpBuilder<(ins "mlir::Value":$lowerBound, "mlir::Value":$upperBound,
       "mlir::Value":$step, CArg<"bool", "false">:$unordered,
       CArg<"bool", "false">:$finalCountValue,
-      CArg<"mlir::ValueRange", "llvm::None">:$iterArgs,
+      CArg<"mlir::ValueRange", "std::nullopt">:$iterArgs,
       CArg<"llvm::ArrayRef<mlir::NamedAttribute>", "{}">:$attributes)>
   ];
 
@@ -2234,7 +2234,7 @@ def fir_IterWhileOp : region_Op<"iterate_while",
     OpBuilder<(ins "mlir::Value":$lowerBound, "mlir::Value":$upperBound,
       "mlir::Value":$step, "mlir::Value":$iterate,
       CArg<"bool", "false">:$finalCountValue,
-      CArg<"mlir::ValueRange", "llvm::None">:$iterArgs,
+      CArg<"mlir::ValueRange", "std::nullopt">:$iterArgs,
       CArg<"llvm::ArrayRef<mlir::NamedAttribute>", "{}">:$attributes)>
   ];