[llvm] [mlir] [Dwarf] Support `__ptrauth` qualifier in metadata nodes (PR #83862)

[David Blaikie via llvm-commits]

================
@@ -1048,6 +1088,39 @@ class DIDerivedType : public DIType {
     return DWARFAddressSpace;
   }
 
+  std::optional<PtrAuthData> getPtrAuthData() const;
+
+  /// \returns The PointerAuth key.
+  std::optional<unsigned> getPtrAuthKey() const {
----------------
dwblaikie wrote:

Are these helpers particularly useful? It seems like they change the usage code from this:
```
if (auto PtrAuthData = getPtrAuthData())
  do_something_with(PtrAuthData->Key());
```
to
```
if (auto Key = getPtrAuthKey())
  do_something_with(*Key);
```

Which doesn't seem like a huge win?

https://github.com/llvm/llvm-project/pull/83862