[llvm] ARM: Remove CPU from computeTargetABI (PR #151983)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic approved this pull request.

Various targets use the module-wide "target CPU" for various decisions, including adding attributes to the object file. Saying it "shouldn't" affect module-level decisions doesn't match reality.

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That said, in this particular case, the triple should be sufficient.  clang canonicalizes the triple: if you try to pass in a triple with the wrong profile, it canonicalizes it to the right architecture.  (For example, if you pass `--target=arm-none-eabi -mcpu=cortex-m0` to clang, it canonicalizes the triple to `thumbv6m-unknown-none-eabi`.)  I think the CPU check is just an artifact of a bunch of refactoring (starting with 1971c3508a3e781104803d750496339460dfac1e), and shouldn't actually be necessary.

LGTM

https://github.com/llvm/llvm-project/pull/151983