[clang] [PAC] Implement function pointer re-signing (PR #98847)

[Akira Hatanaka via cfe-commits]

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+// RUN: %clang_cc1 %s -triple arm64e-apple-ios13 -fptrauth-calls -fptrauth-intrinsics -emit-llvm -o-  -fptrauth-function-pointer-type-discrimination | FileCheck %s
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ahatanak wrote:

Thanks! Please add a line to test linux after this PR is merged.

https://github.com/llvm/llvm-project/pull/98847