[llvm] [SPIRV] Change how to detect OpenCL/Vulkan Env and update tests accordingly. (PR #129689)

[Alexey Bader via llvm-commits]

================
@@ -36,6 +36,10 @@ class StringRef;
 class SPIRVTargetMachine;
 
 class SPIRVSubtarget : public SPIRVGenSubtargetInfo {
+public:
+  // Enum for the SPIR-V environment: OpenCL, Vulkan or Unkwnown.
----------------
bader wrote:

```suggestion
  // Enum for the SPIR-V environment: OpenCL, Vulkan or Unknown.
```
What is the semantic meaning of `Unknown`? Does it mean it could be either OpenCL or Vulkan? Or does it mean "invalid" since it is not set?

https://github.com/llvm/llvm-project/pull/129689