Windows/OS X cross builds generalization and cleanup.

[aszlig]

This is a merge of my cross-building branches for OS X and Windows (MinGW-w64) and this branch is for working on generalization of both cross-builds and also cleaning up old cruft.

Also, again, I'd welcome any comments/ideas/suggestion on that topic (already asked for that in #1876).

The remaining todos/questions for after the merge for 14.04 are:

• Add a stdenv.isDarwinTarget, stdenv.isLinuxTarget and stdenv.isWindowsTarget which essentially are something like for example isWindows = if stdenv ? cross then stdenv.cross.libc == "msvcrt" else stdenv.isWindows, so if you're not cross-compiling, the *Target attribute reflects the native architecture.
• Remove old MinGW(32)-specific stuff. Non-MinGW-w64 builds are broken right now anyway and if noone starts to shed a tear, I'm going to remove it as MinGW-w64 is able to compile to 32 and 64 bit PE.
• Check whether things such as opensslCrossSystem are still necessary and why they were introduced in the first place.
• Enable running of tests using runInWindowsVM and runInMacOSXVM.
• Clean up release-cross.nix.
• Improve cross-building with cmake.
• Evaluate use of --with-sysroot for all cross-architectures in gcc-stage-final (according to the GCC
  docs, the options --with-headers and --with-libs are deprecated).
• Maybe allow to assign/match platform meta attributes with cross targets?

I've added a jobset for native builds and for cross builds on my Hydra. The latter only consists of x86(_64) NixOS machines, so I can't test whether anything breaks something like for example native Darwin builds.

[shlevy]

@aszlig Can you summarize the important changes? There's a lot in here, which is great, but it's a bit hard to review as-is.

[aszlig]

In case of MinGW it's mostly fixup and cleanup away from building with old MinGW(32) towards MinGW-w64 plus fixes of some packages.

For the Darwin part, it's a new cross-target based on XCode and cctools plus again fixes of some packages.

This PR contains the merge (c7bac81) of both of them, because quite a lot of these fixes and the crossbuild implementation share quite a lot in common, so I'm using this branch to clean them up and generalize the repetitious code.

[offlinehacker]

So what does cross builds for osx mean(i lack knowledge about osx)? Will we be able to build packages for osx on linux?

[aszlig]

@offlinehacker: Essentially, yes and that's already possible with this branch, although it needs the mentioned cleanup/generalization before being ready to be merged.

[offlinehacker]

Seems reasonable, i reviewed changes as far as i understood them and they sure look good to me :)

[offlinehacker]

Ok i was testing a few cross builds for mingw, and it works well for me. Can you give/add crossSystem config for darwin?

[aszlig]

Cool, thanks for reviewing/testing, for Darwin I'm currently using:

crossSystem = {
  config = "x86_64-apple-darwin13";
  arch = "x86_64";
  libc = "libSystem";
  platform = {};
  osxMinVersion = "10.7";
  openssl.system = "darwin64-x86_64-cc";
}

[offlinehacker]

Thanks, this works great :)

@aszlig @edolstra: Do you think there's any chance we get cross builds(espeically mingw) with hydra. What i would like to see is building some binaries statically, and have them ready for distribution in different kinds of projects that have needs for having statically built binaries avalible. Now i have to do this with my own hydra instance. One example of this is bunch of projects that use bin-wrapper from nodejs(ex. https://github.com/yeoman/node-optipng-bin) and i've said that i can provide statically built binaries for different platforms. For now i'll be building with my own hydra instance, but it would be great if hydra.nixos.org could build such things :)

[shlevy]

This all looks awesome, is there any more testing or work you need help with?