skarnet.org packages: fix darwin build

The configure scripts have been changed so that `--build` is now the
way to specify (non-cross compiling) build target, which is necessary
on darwin for binary compatibility across darwin versions.

pkgs/tools/system/s6/default.nix

@@ -29,7 +29,7 @@ in stdenv.mkDerivation rec {
     "--with-dynlib=${execline}/lib"
   ]
   ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ])
-  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
+  ++ (stdenv.lib.optional stdenv.isDarwin "--build=${stdenv.system}");
 
   meta = {
     homepage = http://www.skarnet.org/software/s6/;