[clang] [clang][rtsan] Introduce realtime sanitizer codegen and driver (PR #102622)

[Fangrui Song via cfe-commits]

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+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -fsanitize=realtime -emit-llvm -o - %s | FileCheck %s
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MaskRay wrote:

`*-unknown-linux-gnu` is more popular.

`none` could also be used for the OS component and is slightly misleading.

https://github.com/llvm/llvm-project/pull/102622