System values in a link time structure are not legal when compiling to targets other than hlsl/dxil

[lodinukal]

Here is a set of files which can be used to reproduce this https://github.com/lodinukal/slang-link-type-bug-repro.

Code generated for hlsl looks correct, with the system value being passed properly and used:

#line 12832
    float _S1 = float(params_0.inner_0._instance_id_offset_0 + BaseAttributes_0.base_instance_0);

However the code doesn't link when targeting spriv/metal, with it erroring when attempting to legalize the entrypoint parameters (in slang-ir-glsl-legalize.cpp and the corresponding metal file). When debugging, I found that usually the structTypeLayout has at least 1 operand usually, but with linking the module, it had 0. Not sure if that helps.