[clang] [CIR][NFC] Use arrangeFunctionDeclaration to build function types (PR #139787)

[Andy Kaylor via cfe-commits]

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@@ -58,8 +59,9 @@ class RequiredArgs {
   }
 
   static RequiredArgs
-  forPrototypePlus(clang::CanQual<clang::FunctionProtoType> prototype) {
-    return forPrototypePlus(prototype.getTypePtr());
+  forPrototypePlus(clang::CanQual<clang::FunctionProtoType> prototype,
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andykaylor wrote:

That's still not exactly right because `additional` will often be zero.

https://github.com/llvm/llvm-project/pull/139787