[compiler-rt] [compiler-rt][rtsan] Introduce first end to end RTsan lit tests, enable instrumented unit tests (PR #105732)

[Fangrui Song via llvm-commits]

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+// RUN: %clangxx -fsanitize=realtime %s -o %t
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MaskRay wrote:

The directory is about test/rtsan, so any word like "test" "rtsan" does not carry more information.

You can call it `basic.cpp` if you think the readers can start reading this test first.

https://github.com/llvm/llvm-project/pull/105732