[libc++] Mark __cpp_lib_constexpr_memory as being implemented

GitOrigin-RevId: 5d0d465ad4d25398519b85879d61fc126abd641c
diff --git a/include/version b/include/version
index 696a9ef..b13afca 100644
--- a/include/version
+++ b/include/version
@@ -301,7 +301,7 @@
 # define __cpp_lib_constexpr_dynamic_alloc              201907L
 # define __cpp_lib_constexpr_functional                 201907L
 // # define __cpp_lib_constexpr_iterator                   201811L
-// # define __cpp_lib_constexpr_memory                     201811L
+# define __cpp_lib_constexpr_memory                     201811L
 # define __cpp_lib_constexpr_numeric                    201911L
 // # define __cpp_lib_constexpr_string                     201907L
 // # define __cpp_lib_constexpr_string_view                201811L