Xcode: deprecate support for Xcode 4

Help/generator/Xcode.rst

@@ -3,7 +3,9 @@ Xcode
 
 Generate Xcode project files.
 
-This supports Xcode 3.0 and above.
+This supports Xcode 3.0 and above.  Support for Xcode versions prior
+to Xcode 5 is deprecated and will be dropped in a future version of
+CMake.
 
 Toolset Selection
 ^^^^^^^^^^^^^^^^^

Help/release/dev/deprecate-xcode-4.rst

@@ -0,0 +1,6 @@
+deprecate-xcode-4
+-----------------
+
+* The :generator:`Xcode` generator deprecated support for Xcode
+  versions prior to Xcode 5.  Support for those will be dropped in a
+  future version of CMake.