[clang][NFC] documents recent type trait primitives

[cjdb]

Summary

Depends on D149492.

clang/docs/LanguageExtensions.rst

 `Embarcadero C++ type traits
 <http://docwiki.embarcadero.com/RADStudio/Rio/en/Type_Trait_Functions_(C%2B%2B11)_Index>`_.
 
 The following type trait primitives are supported by Clang. Those traits marked
 (C++) provide implementations for type traits specified by the C++ standard;
 ``__X(...)`` has the same semantics and constraints as the corresponding
 ``std::X_t<...>`` or ``std::X_v<...>`` type trait.
 
+* ``__add_lvalue_reference(type)`` (C++)
+* ``__add_pointer(type)`` (C++)
+* ``__add_rvalue_reference(type)`` (C++)
 * ``__array_rank(type)`` (Embarcadero):
   Returns the number of levels of array in the type ``type``:
   ``0`` if ``type`` is not an array type, and
   ``__array_rank(element) + 1`` if ``type`` is an array of ``element``.
 * ``__array_extent(type, dim)`` (Embarcadero):
   The ``dim``'th array bound in the type ``type``, or ``0`` if
   ``dim >= __array_rank(type)``.
 * ``__can_pass_in_regs`` (C++)
   Returns whether a class can be passed in registers under the current
   ABI. This type can only be applied to unqualified class types.
   This is not a portable type trait.
+* ``__decay(type)`` (C++)
 * ``__has_nothrow_assign`` (GNU, Microsoft, Embarcadero):
   Deprecated, use ``__is_nothrow_assignable`` instead.
 * ``__has_nothrow_move_assign`` (GNU, Microsoft):
   Deprecated, use ``__is_nothrow_assignable`` instead.
 * ``__has_nothrow_copy`` (GNU, Microsoft):
   Deprecated, use ``__is_nothrow_constructible`` instead.
 * ``__has_nothrow_constructor`` (GNU, Microsoft):
   Deprecated, use ``__is_nothrow_constructible`` instead.
* ``__is_trivially_equality_comparable`` (Clang): Returns true if comparing two
   value representations.
 * ``__is_unbounded_array`` (C++, GNU, Microsoft, Embarcadero)
 * ``__is_union`` (C++, GNU, Microsoft, Embarcadero)
 * ``__is_unsigned`` (C++, Embarcadero):
   Returns false for enumeration types. Note, before Clang 13, returned true for
   enumeration types if the underlying type was unsigned.
 * ``__is_void`` (C++, Embarcadero)
 * ``__is_volatile`` (C++, Embarcadero)
+* ``__make_signed(type)`` (C++)
+* ``__make_unsigned(type)`` (C++)
 * ``__reference_binds_to_temporary(T, U)`` (Clang):  Determines whether a
   reference of type ``T`` bound to an expression of type ``U`` would bind to a
   materialized temporary object. If ``T`` is not a reference type the result
   is false. Note this trait will also return false when the initialization of
   ``T`` from ``U`` is ill-formed.
-* ``__underlying_type`` (C++, GNU, Microsoft)
+* ``__remove_all_extents(type)`` (C++)
+* ``__remove_const(type)`` (C++)
+* ``__remove_cv(type)`` (C++)
+* ``__remove_cvref(type)`` (C++)
+* ``__remove_extent(type)`` (C++)
+* ``__remove_pointer(type)``(C++)
+* ``__remove_reference(type)`` (C++)
+* ``__remove_restrict(type)`` (C++)
+* ``__remove_volatile(type)`` (C++)
+* ``__underlying_type(type)`` (C++, GNU, Microsoft)
 
 In addition, the following expression traits are supported:
 
 * ``__is_lvalue_expr(e)`` (Embarcadero):
   Returns true if ``e`` is an lvalue expression.
   Deprecated, use ``__is_lvalue_reference(decltype((e)))`` instead.
 * ``__is_rvalue_expr(e)`` (Embarcadero):
   Returns true if ``e`` is a prvalue expression.