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

[Fangrui Song via cfe-commits]

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+// RUN: %clang     -target x86_64-unknown-linux -fsanitize=realtime %s -S -emit-llvm -o - | FileCheck %s
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MaskRay wrote:

Driver tests should only use `-###` to test CC1 options. We don't test different `-O` combinations. It's not useful to test `-flto`

test/CodeGen tests `%clang_cc1`

We generally don't add end-to-end tests.


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