stdenv: start deprecating non-list configureFlags

the motivation for this is to simplify stdenv and ease the job of
reviewers due to them needing to tell contributors about the defacto
rule that configureFlags should be a list of strings

pkgs/stdenv/generic/make-derivation.nix

@@ -331,8 +331,8 @@ else let
 
       # This parameter is sometimes a string, sometimes null, and sometimes a list, yuck
       configureFlags = let inherit (lib) optional elem; in
-        (/**/ if lib.isString configureFlags then [configureFlags]
-         else if configureFlags == null      then []
+        (/**/ if lib.isString configureFlags then lib.warn "String 'configureFlags' is deprecated and will be removed in release 23.05. Please use a list of strings. Derivation name: ${derivationArg.name}, file: ${pos.file or "unknown file"}" [configureFlags]
+         else if configureFlags == null      then lib.warn "Null 'configureFlags' is deprecated and will be removed in release 23.05. Please use a empty list instead '[]'. Derivation name: ${derivationArg.name}, file: ${pos.file or "unknown file"}" []
          else                                     configureFlags)
         ++ optional (elem "build"  configurePlatforms) "--build=${stdenv.buildPlatform.config}"
         ++ optional (elem "host"   configurePlatforms) "--host=${stdenv.hostPlatform.config}"