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

[Oliver Hunt via cfe-commits]

================
@@ -65,6 +65,17 @@ enum class PointerAuthenticationMode : unsigned {
   SignAndAuth
 };
 
+static constexpr llvm::StringLiteral PointerAuthenticationOptionStrip = "strip";
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ojhunt wrote:

ah so what @erichkeane was suggesting is that places needing the string would do

```cpp
   std::string myString = get_the_string_for(thEnum)
```

Though that still leaves me with "where should these functions and enums live?"

It really does not seem like LangOpts is right

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