[HLSL] Fix failing SPIR-V backend tests that specify --target-env vulkan1.3

[kmpeng]

Problem

When SPIRV-Tools is enabled, tests that specify the target environment vulkan1.3 in the validation step fail. The tests are:

• CodeGen/SPIRV/hlsl-intrinsics/SV_GroupIndex.ll (link)
• CodeGen/SPIRV/hlsl-intrinsics/smoothstep.ll (link)

Temporary fix

This PR was a stop gap to get the pipeline green again:
#136343

Long term fix

The current suggestion from @s-perron is to change the tests to not have external functions or variables, e.g. making the functions shader entry points. More discussion is likely needed.

[llvm-beanz]

I've advised @kmpeng to have new SPIR-V tests use --target-env spv1.4 instead of a Vulkan target since that works.

@s-perron we should figure out how we want these tests written for Vulkan and we can circle back to update the test cases.

[s-perron]

Sure. However, we need should try to have the API we are trying to target in the spirv-val step. Many details are left to the target environment. The "universal" environment will simply not check these requirements.

For example, the LocalInvocationIndex in SPIR-V says:

Local invocation index in GLCompute Execution Models. See the client API specification for more detail.

Then you need to know that it is vulkan for the validator to check for API specific requirements:
https://docs.vulkan.org/spec/latest/chapters/interfaces.html#VUID-LocalInvocationIndex-LocalInvocationIndex-04284

The validator may not check everything yet, but it is good to catch it where we can.