[llvm] [llvm] Support building with c++23 (PR #154372)

[A. Jiang via llvm-commits]

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@@ -36,7 +36,7 @@ class MachineFunctionAnalysis
     std::unique_ptr<MachineFunction> MF;
 
   public:
-    Result(std::unique_ptr<MachineFunction> MF) : MF(std::move(MF)) {}
+    Result(std::unique_ptr<MachineFunction> MF);
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frederick-vs-ja wrote:

These changes seems largely related to the addition of `constexpr` to `unique_ptr` in C++23, which caused Clang to require type completeness in more cases.

I guess the completeness requirement is somehow superfluous, see #59292. Perhaps we should mention the that issue in the PR description (which will be used for squashed commit message by default).

https://github.com/llvm/llvm-project/pull/154372