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

[Paulo Matos via llvm-commits]

pmatos wrote:

> > ```
> > * The last lines say `These prefixes are unused...` even if they are used early on.
> > ```
> 
> That's just a sideeffect of some of the prefixes being manually added

Thanks - I will merge this then.

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