[clang] [llvm] [clang][llvm][AArch64] Set hardening fn attrs on synthetic functions (PR #211013)

[Daniil Kovalev via cfe-commits]

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+// RUN: %clang_cc1 -triple arm64-apple-ios   -coverage-data-file=/dev/null                                -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,OFF
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kovdan01 wrote:

I've left this test as "end-to-end" test for the original reproducer the issue was discovered on, and also added a test in llvm/test per your suggestion - thanks for raising this concern.

Also note that there are several other tests in clang/test/CodeGen which enable `-coverage-data-file=/dev/null` so I believe it should be fine

https://github.com/llvm/llvm-project/pull/211013