miniupnpc: fix on darwin

For some reason miniupnpc needs libtool for static linking. Probably not ideal
but it’s doing similar on other platforms as well (using ar).

pkgs/tools/networking/miniupnpc/default.nix

···
-{ stdenv, fetchurl }:
+{ stdenv, fetchurl, which, cctools }:
 
 let
   generic = { version, sha256 }:
···
         inherit sha256;
       };
 
+      nativeBuildInputs = [] ++
+        stdenv.lib.optionals stdenv.isDarwin [ which cctools ];
+
       patches = stdenv.lib.optional stdenv.isFreeBSD ./freebsd.patch;
 
       doCheck = !stdenv.isFreeBSD;
 
-      installFlags = "PREFIX=$(out) INSTALLPREFIX=$(out)";
+      makeFlags = "PREFIX=$(out) INSTALLPREFIX=$(out)";
 
       meta = {
         homepage = http://miniupnp.free.fr/;

pkgs/top-level/all-packages.nix

···
 
   minissdpd = callPackage ../tools/networking/minissdpd { };
 
-  inherit (callPackage ../tools/networking/miniupnpc { })
+  inherit (callPackage ../tools/networking/miniupnpc
+            { inherit (darwin) cctools; })
     miniupnpc_1 miniupnpc_2;
   miniupnpc = miniupnpc_1;