[libcxx] [llvm] [libc++] Fix optional<T>::transform to optional<T&> (GH#220332) (PR #220500)

[A. Jiang via llvm-commits]

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@@ -80,6 +80,26 @@ static bool isNullOrUndef(const Constant *C) {
   return true;
 }
 
+/// Return true if the constant contains any undef or poison sub-elements,
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frederick-vs-ja wrote:

If this PR intends to fix libc++, please revert the changes to LLVM components.

https://github.com/llvm/llvm-project/pull/220500