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/applications/virtualization/bochs/default.nix

@@ -146,7 +146,7 @@ stdenv.mkDerivation rec {
   NIX_CFLAGS_COMPILE="-I${gtk}/include/gtk-2.0/ -I${libtool}/include/";
   NIX_LDFLAGS="-L${libtool}/lib";
 
-  hardening_format = false;
+  hardeningDisable = [ "format" ];
 
   meta = with stdenv.lib; {
     description = "An open-source IA-32 (x86) PC emulator";