[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/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
=================