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

[Simon Pilgrim via llvm-commits]

================
@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 3
 ; RUN: llc -O0 -mtriple=spirv32-unknown-unknown --spirv-extensions=SPV_INTEL_optnone %s -o - | FileCheck %s --check-prefix=CHECK-EXTENSION
 ; RUN: llc -O0 -mtriple=spirv32-unknown-unknown %s -o - | FileCheck %s --check-prefix=CHECK-NO-EXTENSION
----------------
RKSimon wrote:

Can you add a common prefix to ensure its working correctly?
```
; RUN: llc -O0 -mtriple=spirv32-unknown-unknown --spirv-extensions=SPV_INTEL_optnone %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-EXTENSION
; RUN: llc -O0 -mtriple=spirv32-unknown-unknown %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-NO-EXTENSION
```

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