[clang-tools-extra] [clang-tidy] Add documentation and smoke test for CUDA (PR #173699)

[Carlos Galvez via cfe-commits]

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+// RUN: clang-tidy %s -checks='-*,modernize-use-nullptr' -- \
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carlosgalvezp wrote:

It should be possible to use `check_clang_tidy` I think. We'll need that to work if we add cuda-specific checks in the future.

It probably needs some update to consider .cu extensions the same as .cpp extensions.

https://github.com/llvm/llvm-project/pull/173699