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/os-specific/linux/disk-indicator/default.nix

@@ -19,7 +19,8 @@ stdenv.mkDerivation {
   buildPhase = "make -f makefile";
 
   NIX_CFLAGS_COMPILE = "-Wno-error=cpp";
-  hardening_fortify = false;
+
+  hardeningDisable = [ "fortify" ];
 
   installPhase = ''
     mkdir -p "$out/bin"