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

[Paulo Matos via llvm-commits]

pmatos wrote:

> The ':' is added because that's the default value of `func_name_separator` if it's not set by the regex. I was suggesting to include an empty capture in the regex so that `func_name_separator` is set to the empty string instead.

Ah yes, I understand what you are saying and I see you have in your suggested RE you have `(?P<func_name_separator>)` but that will still result in:
```
; CHECK-LABEL: _Z3foov
; CHECK:       %4 = OpFunction %2 DontInline %3
; CHECK-NEXT:    %5 = OpLabel
; CHECK-NEXT:    OpReturn
; CHECK-NEXT:    OpFunctionEnd
```

but SPIRV issues no labels. The odd thing (for me) is that:

* the test passes even with a `CHECK-LABEL: _Z3foov` even if there's no label;
* The last lines say `These prefixes are unused...` even if they are used early on.


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