Revert "[libc++] Use _If for conditional_t"

[jyknight]

Reverts #96193

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: James Y Knight (jyknight)

Changes

Reverts llvm/llvm-project#96193

---

Full diff: https://github.com/llvm/llvm-project/pull/96843.diff

1 Files Affected:

• (modified) libcxx/include/__type_traits/conditional.h (+5-4)

diff --git a/libcxx/include/__type_traits/conditional.h b/libcxx/include/__type_traits/conditional.h
index 7d5849ee824e3..5b5445a837427 100644
--- a/libcxx/include/__type_traits/conditional.h
+++ b/libcxx/include/__type_traits/conditional.h
@@ -44,14 +44,15 @@ struct _LIBCPP_TEMPLATE_VIS conditional<false, _If, _Then> {
   using type _LIBCPP_NODEBUG = _Then;
 };
 
-template <bool _Bp, class _IfRes, class _ElseRes>
-using __conditional_t _LIBCPP_NODEBUG = _If<_Bp, _IfRes, _ElseRes>;
-
 #if _LIBCPP_STD_VER >= 14
 template <bool _Bp, class _IfRes, class _ElseRes>
-using conditional_t _LIBCPP_NODEBUG = __conditional_t<_Bp, _IfRes, _ElseRes>;
+using conditional_t _LIBCPP_NODEBUG = typename conditional<_Bp, _IfRes, _ElseRes>::type;
 #endif
 
+// Helper so we can use "conditional_t" in all language versions.
+template <bool _Bp, class _If, class _Then>
+using __conditional_t _LIBCPP_NODEBUG = typename conditional<_Bp, _If, _Then>::type;
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___TYPE_TRAITS_CONDITIONAL_H

[MaskRay]

The description should ideally mention the reason.

[ldionne]

This was already reverted in 3748162.