[clang] [libcxx] [Clang][libc++] Implement __is_nothrow_convertible and use it in libc++ (PR #80436)

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git-clang-format --diff a1df10da59e8eb0c1d90df81bf9000d2f7869328 dc3aafe0e3bd2e20121440efd8efa86263bd6b4b -- clang/lib/Sema/SemaExprCXX.cpp clang/test/SemaCXX/type-traits.cpp libcxx/include/__type_traits/is_nothrow_convertible.h
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View the diff from clang-format here.
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diff --git a/libcxx/include/__type_traits/is_nothrow_convertible.h b/libcxx/include/__type_traits/is_nothrow_convertible.h
index 2f9b4f953c..bfc5a94cba 100644
--- a/libcxx/include/__type_traits/is_nothrow_convertible.h
+++ b/libcxx/include/__type_traits/is_nothrow_convertible.h
@@ -26,7 +26,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER >= 20
 
-#if __has_builtin(__is_nothrow_convertible)
+#  if __has_builtin(__is_nothrow_convertible)
 
 template <class _Tp, class _Up>
 struct is_nothrow_convertible : bool_constant<__is_nothrow_convertible(_Tp, _Up)> {};
@@ -34,7 +34,7 @@ struct is_nothrow_convertible : bool_constant<__is_nothrow_convertible(_Tp, _Up)
 template <class _Tp, class _Up>
 inline constexpr bool is_nothrow_convertible_v = __is_nothrow_convertible(_Tp, _Up);
 
-#else // __has_builtin(__is_nothrow_convertible)
+#  else // __has_builtin(__is_nothrow_convertible)
 
 template <typename _Tp>
 void __test_noexcept(_Tp) noexcept;
@@ -53,7 +53,7 @@ struct is_nothrow_convertible
 template <typename _Fm, typename _To>
 inline constexpr bool is_nothrow_convertible_v = is_nothrow_convertible<_Fm, _To>::value;
 
-#endif // __has_builtin(__is_nothrow_convertible)
+#  endif // __has_builtin(__is_nothrow_convertible)
 
 #endif // _LIBCPP_STD_VER >= 20
 

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https://github.com/llvm/llvm-project/pull/80436