[llvm] [DXIL][Doc] Update specification of to use TableGen list instead of dag (PR #99055)

[Justin Bogner via llvm-commits]

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@@ -93,25 +93,30 @@ attributes are specified as fields of the ``DXILOp`` class as described below.
         class DXILOpClass;
 
    Concrete operation records, such as ``unary`` are defined by inheriting from ``DXILOpClass``.
-6. Return and argument types of the operation are represented as ``dag``s using the
-   special markers ``out`` and ``ins``. An overload type, if supported by the operation, is
+6. A non-``void`` return type of the operation is represented as a list with one ``LLVMType``. 
+   A ``void`` return is represented as a null-list, ``[]``.
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bogner wrote:

Why not just use `llvm_void_ty` for a void return type instead of this being a list?

https://github.com/llvm/llvm-project/pull/99055