Add SPIR-V backend support for the HLSL SV_DispatchThreadID semantic
attribute, which is lowered to a @llvm.dx.thread.id intrinsic in LLVM
IR. In the SPIR-V backend, this is now correctly translated to a
`GlobalInvocationId` builtin variable.
Fixes#82534
Support SV_DispatchThreadID attribute.
Translate it into dx.thread.id in clang codeGen.
Reviewed By: beanz, aaron.ballman
Differential Revision: https://reviews.llvm.org/D133983
Semantic parameters aren't passed as actual parameters, instead they are
populated from intrinsics which are generally lowered to reads from
dedicated hardware registers.
This change modifies clang CodeGen to emit the intrinsic calls and
populate the parameter's LValue with the result of the intrinsic call
for SV_GroupIndex.
The result of this is to make the actual passed argument ignored, which
will make it easy to clean up later in an IR pass.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D131203
