stdenv: promote zerocallusedregs to defaultHardeningFlags

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

@@ -45,6 +45,7 @@
     "relro"
     "stackprotector"
     "strictoverflow"
+    "zerocallusedregs"
   ] ++ lib.optional (with stdenvNoCC;
     # Musl-based platforms will keep "pie", other platforms will not.
     # If you change this, make sure to update section `{#sec-hardening-in-nixpkgs}`

pkgs/top-level/stage.nix

@@ -292,7 +292,6 @@ let
           pkgsExtraHardening = super';
           stdenv = super'.withDefaultHardeningFlags (
             super'.stdenv.cc.defaultHardeningFlags ++ [
-              "zerocallusedregs"
               "trivialautovarinit"
             ]
           ) super'.stdenv;