[clang] [Clang] allow [[msvc::constexpr]] usage outside the std namespace (PR #119153)

[Richard Dzenis via cfe-commits]

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RIscRIpt wrote:

I don't think so.

Ah, I forgot I previously added `clang/test/AST/ms-constexpr.cpp`, so having your new `ms-constexpr-new.cpp` makes sense (sorry for confusion).

But I still would like to see a test in `clang/test/SemaCXX/ms-constexpr-new.cpp` that placement new can be called outside of `std` namespace (in non c++26 mode) when used in `[[msvc::constexpr]]` context.

https://github.com/llvm/llvm-project/pull/119153