[llvm] ConstraintSystem: replace data structure with Matrix (PR #98895)

[Jakub Kuderski via llvm-commits]

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@@ -59,6 +60,8 @@ namespace llvm {
     /// The number of elements.
     size_type Length = 0;
 
+    friend MutableRowView<T>;
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kuhar wrote:

Why do we need this?

https://github.com/llvm/llvm-project/pull/98895