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

[Simon Pilgrim via llvm-commits]

RKSimon 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


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