[clang] [clang][PAC][NFC] Provide addition support macros to ptrauth.h (PR #161027)

[Oliver Hunt via cfe-commits]

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@@ -241,6 +260,18 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
 #define ptrauth_type_discriminator(__type)                                     \
   __builtin_ptrauth_type_discriminator(__type)
 
+/* Compute the constant discriminator used by Clang to sign pointers with the
+   given C function pointer type.
+
+   A call to this function is an integer constant expression. */
+#if __has_feature(ptrauth_function_pointer_type_discrimination)
+#define ptrauth_function_pointer_type_discriminator(__type)                    \
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ojhunt wrote:

it's kind of awkwardly named, but is used extensively :-/

https://github.com/llvm/llvm-project/pull/161027