[clang] [CIR] Add custom constructor declaration to CIR lowering TableGen (PR #176664)

[Sirui Mu via cfe-commits]

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@@ -77,17 +77,35 @@ class LLVMLoweringInfo {
   string llvmOp = "";
 }
 
+class loweringBuilders<dag p, code b = ""> {
+  dag dagParams = p;
+  code body = b;
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Lancern wrote:

Do we have a use case yet that requires the body to be specified?

https://github.com/llvm/llvm-project/pull/176664