032900eb30
This pr adds the equivalent validation of `llvm.loop` metadata that is
[done in
DXC](8f21027f2a/lib/DxilValidation/DxilValidation.cpp (L3010)).
This is done as follows:
- Add `llvm.loop` to the metadata allow-list in `DXILTranslateMetadata`
- Iterate through all `llvm.loop` metadata nodes and strip all
incompatible ones
- Raise an error for ill-formed nodes that are compatible with DXIL
Resolves: https://github.com/llvm/llvm-project/issues/137387