[llvm] [UpdateTestChecks] Add support for SPIRV in update_llc_test_checks.py (PR #66213)

[Paulo Matos via llvm-commits]

pmatos wrote:

> Could we just emit a different label format that matches the comment for spirv? Having to pass the flag seems a bit awkward

I would love to be able to do that but the `check_label_format` string is sufficiently hardcoded that changing this feels like it could be potentially a pandora's box:
https://github.com/llvm/llvm-project/blob/7f3610ac69191a2a445fa9b4b947019a2fd51fb1/llvm/utils/UpdateTestChecks/asm.py#L585

Happy to hear any ideas that might ease changing this without breaking other stuff.

https://github.com/llvm/llvm-project/pull/66213