[llvm] [LegacyPM][DirectX] Add legacy scalarizer back for use in the DirectX backend (PR #107427)

[Farzon Lotfi via llvm-commits]

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@@ -340,8 +341,33 @@ class ScalarizerVisitor : public InstVisitor<ScalarizerVisitor, bool> {
   const unsigned ScalarizeMinBits;
 };
 
+class ScalarizerLegacyPass : public FunctionPass {
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farzonl wrote:

@nikic or @boomanaiden154 would you be willing to approve this PR. 

https://github.com/llvm/llvm-project/pull/107427