[llvm] [AMDGPU] Introduce custom MIR formatting for s_wait_alu (PR #176316)

[via llvm-commits]

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vporpo wrote:

This lack of whitespace is needed here because of the `--strict-whitespace` FileCheck option, which is required for checking the position of the arrow that points to the error column `   ^`.

https://github.com/llvm/llvm-project/pull/176316