Use general hardening flag toggle lists

The following parameters are now available:

  * hardeningDisable
    To disable specific hardening flags
  * hardeningEnable
    To enable specific hardening flags

Only the cc-wrapper supports this right now, but these may be reused by
other wrappers, builders or setup hooks.

cc-wrapper supports the following flags:

  * fortify
  * stackprotector
  * pie (disabled by default)
  * pic
  * strictoverflow
  * format
  * relro
  * bindnow

pkgs/build-support/cc-wrapper/default.nix

@@ -234,6 +234,7 @@ stdenv.mkDerivation {
       rm $out/nix-support/setup-hook.tmp
 
       substituteAll ${./add-flags} $out/nix-support/add-flags.sh
+      cp -p ${./add-hardening} $out/nix-support/add-hardening.sh
       cp -p ${./utils.sh} $out/nix-support/utils.sh
     ''
     + extraBuildCommands;