Second half of C++17's splicing maps and sets

This commit adds a merge member function to all the map and set containers,
which splices nodes from the source container. This completes support for
P0083r3.

Differential revision: https://reviews.llvm.org/D48896

llvm-svn: 345744
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 5c4e07ae5c6f7f467b436f1b24f41ef4cf9897b3
diff --git a/include/version b/include/version
index 6e61693..aca84f8 100644
--- a/include/version
+++ b/include/version
@@ -110,6 +110,7 @@
 # define __cpp_lib_filesystem                           201703L
 # define __cpp_lib_invoke                               201411L
 # define __cpp_lib_void_t                               201411L
+# define __cpp_lib_node_extract                         201606L
 #endif
 
 #if _LIBCPP_STD_VER > 17