stdenv: warn about use of inherited lib

pkgs/stdenv/generic/default.nix

@@ -152,9 +152,12 @@ let
         inherit lib config stdenv;
       }) mkDerivation;
 
-      # For convenience, bring in the library functions in lib/ so
+      # Slated for deprecation in 21.11
-      # packages don't have to do that themselves.
+      lib = builtins.trace ( "Warning: `stdenv.lib` is deprecated "
-      inherit lib;
+                           + "and will be removed in the next release. "
+                           + "Please use `pkgs.lib` instead. "
+                           + "For more information see https://github.com/NixOS/nixpkgs/issues/108938")
+                           lib;
 
       inherit fetchurlBoot;