[clang] [clang][PAC] ptrauth_qualifier and ptrauth_intrinsic should only be available on Darwin (PR #153912)

[Aaron Ballman via cfe-commits]

================
@@ -144,6 +144,11 @@ New Compiler Flags
 Deprecated Compiler Flags
 -------------------------
 
+- Use of `__has_feature` to detect the `ptrauth_qualifier` and `ptrauth_intrinsics`
+  features has been deprecated, and is restricted to the arm64e target only. The
+  correct method to check for these features is to test for the `__PTRAUTH__`
+  macro.
----------------
AaronBallman wrote:

```suggestion
- Use of ``__has_feature`` to detect the ``ptrauth_qualifier`` and ``ptrauth_intrinsics``
  features has been deprecated, and is restricted to the arm64e target only. The
  correct method to check for these features is to test for the ``__PTRAUTH__``
  macro.
```

https://github.com/llvm/llvm-project/pull/153912