[libc++] [C++2b] [P1682] Add to_underlying.

* https://wg21.link/P1682

Reviewed By: ldionne, Mordante, #libc

Differential Revision: https://reviews.llvm.org/D97365

GitOrigin-RevId: 43e421417378bab378eccdf88a66a0a46304fa13
diff --git a/docs/Cxx2bStatusPaperStatus.csv b/docs/Cxx2bStatusPaperStatus.csv
index c6efa20..79b5db0 100644
--- a/docs/Cxx2bStatusPaperStatus.csv
+++ b/docs/Cxx2bStatusPaperStatus.csv
@@ -4,7 +4,7 @@
 "`P1048R1 <https://wg21.link/P1048R1>`__","LWG","A proposal for a type trait to detect scoped enumerations","Autumn 2020","|Complete|","12.0"
 "`P1679R3 <https://wg21.link/P1679R3>`__","LWG","string contains function","Autumn 2020","|Complete|","12.0"
 "","","","","",""
-"`P1682R3 <https://wg21.link/P1682R3>`__","LWG","std::to_underlying for enumerations","February 2021","",""
+"`P1682R3 <https://wg21.link/P1682R3>`__","LWG","std::to_underlying for enumerations","February 2021","|Complete|","13.0"
 "`P2017R1 <https://wg21.link/P2017R1>`__","LWG","Conditionally borrowed ranges","February 2021","",""
 "`P2160R1 <https://wg21.link/P2160R1>`__","LWG","Locks lock lockables","February 2021","",""
 "`P2162R2 <https://wg21.link/P2162R2>`__","LWG","Inheriting from std::variant","February 2021","",""
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index 77010b5..693a668 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -301,5 +301,7 @@
     ``__cpp_lib_stdatomic_h``                         *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_string_contains``                     ``202011L``
+    ------------------------------------------------- -----------------
+    ``__cpp_lib_to_underlying``                       ``202102L``
     ================================================= =================