stdenv: warn about use of stdenv.glibc

TODO was added in
119920faa6

pkgs/stdenv/linux/default.nix

@@ -398,8 +398,11 @@ in
       inherit (prevStage.stdenv) fetchurlBoot;
 
       extraAttrs = {
-        # TODO: remove this!
+        # remove before 22.11
-        inherit (prevStage) glibc;
+        glibc = lib.warn
+          ( "`stdenv.glibc` is deprecated and will be removed in release 22.11."
+           + " Please use `pkgs.glibc` instead.")
+          prevStage.glibc;
 
         inherit bootstrapTools;
         shellPackage = prevStage.bash;