[clang] [Clang][ARM][AArch64] Add branch protection attributes to the defaults. (PR #83277)

[via cfe-commits]

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+// RUN: %clang_cc1 -triple aarch64-none-none -mbranch-target-enforce -msign-return-address=all -fcxx-exceptions -fexceptions -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK
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DanielKristofKiss wrote:

> perhaps it's time to add CodeGenCXX/AArch64/ ? We have more target-specific directories under CodeGen.
> Then the weird arm64- prefix (not recommended for ELF/Arm official) can be removed.

I'll create a NFC patch that cleans all of these up. (also in CodeGen where we have directories and prefixed files too.) 

> You can remove -fcxx-exceptions -fexceptions since they are unused

`__clang_call_terminate` is only generated when the exceptions are enabled. Clang generates the definition for it too and the test checks the right attributes for it.

> -triple aarch64-none-nonecan just be-triple aarch64`.

ack

https://github.com/llvm/llvm-project/pull/83277