[clang] [Arm64EC][clang] Implement varargs support in clang. (PR #152411)

[Daniel Paoliello via cfe-commits]

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@@ -1409,6 +1409,12 @@ class WinX86_64ABIInfo : public ABIInfo {
     return isX86VectorCallAggregateSmallEnough(NumMembers);
   }
 
+  ABIArgInfo classifyArgForArm64ECVarArg(QualType Ty) const override {
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dpaoliello wrote:

Let's add some comments to explain this for anyone else who is wondering why there's Arm in their X86, I'm not sure that factoring out this code really helps with readability or maintainability.

https://github.com/llvm/llvm-project/pull/152411