[libc++] Remove a few workarounds for old Clang versions (#143858)

Author: philnik777

libcxx/include/__config

@@ -505,13 +505,6 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_HIDE_FROM_ABI_AFTER_V1 _LIBCPP_HIDE_FROM_ABI
 #  endif
 
-// TODO: Remove this workaround once we drop support for Clang 16
-#  if __has_warning("-Wc++23-extensions")
-#    define _LIBCPP_CLANG_DIAGNOSTIC_IGNORED_CXX23_EXTENSION _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wc++23-extensions")
-#  else
-#    define _LIBCPP_CLANG_DIAGNOSTIC_IGNORED_CXX23_EXTENSION _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wc++2b-extensions")
-#  endif
-
 // Clang modules take a significant compile time hit when pushing and popping diagnostics.
 // Since all the headers are marked as system headers unless _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER is defined, we can
 // simply disable this pushing and popping when _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER isn't defined.
@@ -522,7 +515,7 @@ typedef __char32_t char32_t;
       _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wc++14-extensions")                                                           \
       _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wc++17-extensions")                                                           \
       _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wc++20-extensions")                                                           \
-      _LIBCPP_CLANG_DIAGNOSTIC_IGNORED_CXX23_EXTENSION                                                                 \
+      _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wc++23-extensions")                                                           \
       _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wc++14-extensions")                                                             \
       _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wc++17-extensions")                                                             \
       _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wc++20-extensions")                                                             \

libcxx/include/__utility/pair.h

@@ -209,21 +209,12 @@ struct pair
 #  endif
 
 #  if _LIBCPP_STD_VER >= 23
-  // TODO: Remove this workaround in LLVM 20. The bug got fixed in Clang 18.
-  // This is a workaround for http://llvm.org/PR60710. We should be able to remove it once Clang is fixed.
-  template <class _PairLike>
-  _LIBCPP_HIDE_FROM_ABI static constexpr bool __pair_like_explicit_wknd() {
-    if constexpr (__pair_like_no_subrange<_PairLike>) {
-      return !is_convertible_v<decltype(std::get<0>(std::declval<_PairLike&&>())), first_type> ||
-             !is_convertible_v<decltype(std::get<1>(std::declval<_PairLike&&>())), second_type>;
-    }
-    return false;
-  }
-
   template <__pair_like_no_subrange _PairLike>
     requires(is_constructible_v<first_type, decltype(std::get<0>(std::declval<_PairLike &&>()))> &&
              is_constructible_v<second_type, decltype(std::get<1>(std::declval<_PairLike &&>()))>)
-  _LIBCPP_HIDE_FROM_ABI constexpr explicit(__pair_like_explicit_wknd<_PairLike>()) pair(_PairLike&& __p)
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit(
+      !is_convertible_v<decltype(std::get<0>(std::declval<_PairLike&&>())), first_type> ||
+      !is_convertible_v<decltype(std::get<1>(std::declval<_PairLike&&>())), second_type>) pair(_PairLike&& __p)
       : first(std::get<0>(std::forward<_PairLike>(__p))), second(std::get<1>(std::forward<_PairLike>(__p))) {}
 #  endif