Merge 'mingw-w64' and 'darwin' into cross-win-osx.

Both branches have quite a lot in common, so it's time for a merge and
do the cleanups with respect to both implementations and also generalize
both implementations as much as possible.

This also closes #1876.

Conflicts:
	pkgs/development/interpreters/lua-5/5.2.nix
	pkgs/development/libraries/SDL/default.nix
	pkgs/development/libraries/glew/default.nix
	pkgs/top-level/all-packages.nix

pkgs/os-specific/windows/mingw-w64/default.nix

@@ -1,30 +1,30 @@
-{stdenv, fetchurl, binutilsCross ? null, gccCross ? null, onlyHeaders ? false}:
+{ stdenv, fetchurl, binutilsCross ? null, gccCross ? null
+, onlyHeaders ? false
+, onlyPthreads ? false
+}:
 
 let
-  name = "mingw-w64-2.0.3";
+  name = "mingw-w64-3.1.0";
 in
 stdenv.mkDerivation (rec {
   inherit name;
 
   src = fetchurl {
-    url = "mirror://sourceforge/mingw-w64/mingw-w64-v2.0.3.tar.gz";
-    sha256 = "043jk6z90f9pxs9kfn6ckh2vlnbgcv6yfbp5ybahrj3z58dcijp5";
+    url = "mirror://sourceforge/mingw-w64/mingw-w64-v3.1.0.tar.bz2";
+    sha256 = "1lhpw381gc59w8b1r9zzdwa9cdi2wx6qx7s6rvajapmbw7ksgrzc";
   };
-
-  # I don't know what's that $host directory about, I put the
-  # files inside include as usual.
-  postInstall = ''
-    rmdir $out/include
-    mv $out/x86_64-w64-mingw32/* $out
-    rm -R $out/x86_64-w64-mingw32
-  '';
 } //
 (if onlyHeaders then {
   name = name + "-headers";
-  preConfingure = ''
+  preConfigure = ''
     cd mingw-w64-headers
   '';
-  configureFlags = "--without-crt --host=x86_64-w64-mingw32";
+  configureFlags = "--without-crt";
+} else if onlyPthreads then {
+  name = name + "-pthreads";
+  preConfigure = ''
+    cd mingw-w64-libraries/winpthreads
+  '';
 } else {
   buildInputs = [ gccCross binutilsCross ];