[libcxx][type_traits] remove `std::is_literal_type` and `std::result_of` for C++20

C++17 deprecated `std::is_literal_type` and `std::result_of`, C++20 removed them.

Implements parts of:
    * P0174R2 'Deprecating Vestigial Library Parts in C++17'.
    * P0619R4 'Reviewing Deprecated Facilities of C++17 for C++20'.

Reviewed By: ldionne, Mordante, Quuxplusone, #libc

Differential Revision: https://reviews.llvm.org/D102992

NOKEYCHECK=True
GitOrigin-RevId: 2ff5a56e1ab2a95c36d3c5d2bef7c585125718ae
diff --git a/docs/Cxx2aStatus.rst b/docs/Cxx2aStatus.rst
index 8bbf7d8..ae23daf 100644
--- a/docs/Cxx2aStatus.rst
+++ b/docs/Cxx2aStatus.rst
@@ -42,7 +42,7 @@
 

    .. [#note-P0600] P0600: The missing bits in P0600 are in |sect|\ [mem.res.class], |sect|\ [mem.poly.allocator.class], and |sect|\ [container.node.overview].

    .. [#note-P0966] P0966: It was previously erroneously marked as complete in version 8.0. See `bug 45368 <https://llvm.org/PR45368>`__.

-   .. [#note-P0619] P0619: Only sections D.8, D.9, and D.10 are implemented. Sections D.4, D.7, D.11, D.12, and D.14 remain undone.

+   .. [#note-P0619] P0619: Only sections D.8, D.9, D.10 and D.13 are implemented. Sections D.4, D.7, D.11, D.12, and D.14 remain undone.

    .. [#note-P0883] P0883: shared_ptr and floating-point changes weren't applied as they themselves aren't implemented yet.

 

 

diff --git a/docs/UsingLibcxx.rst b/docs/UsingLibcxx.rst
index 31ec90c..b967c98 100644
--- a/docs/UsingLibcxx.rst
+++ b/docs/UsingLibcxx.rst
@@ -266,6 +266,9 @@
 **_LIBCPP_ENABLE_CXX20_REMOVED_RAW_STORAGE_ITERATOR**:
   This macro is used to re-enable `raw_storage_iterator`.
 
+**_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS**:
+  This macro is used to re-enable `is_literal_type`, `is_literal_type_v`, 
+  `result_of` and `result_of_t`.
 
 Libc++ Extensions
 =================