[libcxx] [llvm] Add C++23 stacktrace (P0881R7) (PR #136528)

[A. Jiang via llvm-commits]

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@@ -570,7 +570,7 @@ _LIBCPP_HIDE_FROM_ABI _Stream&& operator<<(_Stream&& __os, const _Tp& __x) {
 }
 
 template <class _CharT, class _Traits, class _Allocator>
-basic_ostream<_CharT, _Traits>&
+_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
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frederick-vs-ja wrote:

Why is this `operator<<` touched? IIUC this should belong to another patch.

https://github.com/llvm/llvm-project/pull/136528