Replace None with std::nullopt in comments (NFC)

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

clang-tools-extra/pseudo/include/clang-pseudo/DirectiveTree.h

@@ -80,7 +80,7 @@ struct DirectiveTree {
     /// The directive terminating the conditional, should be #endif.
     Directive End;
     /// The index of the conditional branch we chose as active.
-    /// None indicates no branch was taken (e.g. #if 0 ... #endif).
+    /// std::nullopt indicates no branch was taken (e.g. #if 0 ... #endif).
     /// The initial tree from `parse()` has no branches marked as taken.
     /// See `chooseConditionalBranches()`.
     std::optional<unsigned> Taken;

llvm/include/llvm/DebugInfo/DWARF/DWARFLocationExpression.h

@@ -19,7 +19,7 @@ class raw_ostream;
 /// Typically used in DW_AT_location attributes to describe the location of
 /// objects.
 struct DWARFLocationExpression {
-  /// The address range in which this expression is valid. None denotes a
+  /// The address range in which this expression is valid. std::nullopt denotes a
   /// default entry which is valid in addresses not covered by other location
   /// expressions, or everywhere if there are no other expressions.
   std::optional<DWARFAddressRange> Range;

llvm/include/llvm/ExecutionEngine/RuntimeDyldChecker.h

@@ -172,7 +172,7 @@ public:
                                                   bool LocalAddress);
 
   /// If there is a section at the given local address, return its load
-  /// address, otherwise return none.
+  /// address, otherwise return std::nullopt.
   std::optional<uint64_t> getSectionLoadAddress(void *LocalAddress) const;
 
 private:

llvm/include/llvm/Transforms/IPO/Attributor.h

@@ -5554,8 +5554,8 @@ struct AAPointerInfo : public AbstractAttribute {
     /// The instruction responsible for the access.
     Instruction *RemoteI;
 
-    /// The value written, if any. `llvm::none` means "not known yet", `nullptr`
-    /// cannot be determined.
+    /// The value written, if any. `std::nullopt` means "not known yet",
+    /// `nullptr` cannot be determined.
     std::optional<Value *> Content;
 
     /// Set of potential ranges accessed from the base pointer.

polly/include/polly/Support/ScopHelper.h

@@ -522,7 +522,7 @@ bool hasDebugCall(ScopStmt *Stmt);
 ///   !{ !"Name" }
 ///
 /// Then `nullptr` is set to mark the property is existing, but does not carry
-/// any value. If the property does not exist, `None` is returned.
+/// any value. If the property does not exist, `std::nullopt` is returned.
 std::optional<llvm::Metadata *> findMetadataOperand(llvm::MDNode *LoopMD,
                                                     llvm::StringRef Name);