[clang] [clang][PAC] add support for options parameter to __ptrauth (PR #136828)

[Aaron Ballman via cfe-commits]

================
@@ -327,6 +330,27 @@ a discriminator determined as follows:
   is ``ptrauth_blend_discriminator(&x, discriminator)``; see
   `ptrauth_blend_discriminator`_.
 
+``ptrauth_qualifier_options``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The options parameter to the ``__ptrauth`` qualifier is a string of comma
+separated modifiers to the normal authentication behavior. Currently supported
+options are
+
+- Authentication mode: This is one of ``strip``, ``sign-and-strip``, and
+  ``sign-and-auth``. The ability to modify this behavior is intended to support
+  staging ABI changes. The ``strip`` mode results in the PAC bits of a value
+  being stripped from any value and disabled any other authentication
+  operations. ``sign-and-strip`` strips an authenticated on read, but will
+  ensure a correct signature is set on assignment. Finally ``sign-and-auth`` is
+  the default mode, and provides full protection for the value.
+
+- ``authenticates-null-values``: By default the __ptrauth qualifier does not
----------------
AaronBallman wrote:

```suggestion
- ``authenticates-null-values``: By default the ``__ptrauth`` qualifier does not
```

https://github.com/llvm/llvm-project/pull/136828