Get glib, gtk+, harfbuzz and pango working on Darwin

[jwiegley]

With this patch I'm able to build the threadscope utility for Haskell.

Note that Xquartz must be installed on Mavericks, as 10.9 does not ship with X11 anymore. I built against Xquartz 2.7.5, the latest version.

[vcunat]

There's something wrong around iconv + nixpkgs + darwin. Our libiconvOrEmpty (&friends) assumes that there's no libiconv without glibc, but to me it seems that darwin distributes one, which creates these collisions. However, I'm not sure if user is required to install something to have it (Xcode?) https://developer.apple.com/library/mac/documentation/Darwin/Reference/Manpages/man3/iconv.3.html

[jwiegley]

Yes, darwin does distribute one.

[peti]

Has this libiconv always been around on Darwin, or is that maybe a new addition from one of the recent OS updates?

[jwiegley]

I'm not sure how long it's been there. It's in /usr/lib/libiconv.2.4.0.dylib on Mavericks.

[peti]

If we want to rely on the native iconv library, then we also need a native iconv executable. Does Darwin have that iconv in $PATH? If so, we should probably add it in pkgs/build-support/native-darwin-cctools-wrapper/default.nix and change the libiconv-* attributes to assume that we have a native one on Darwin.

[jwiegley]

Yes, it's at /usr/bin/iconv.

[vcunat]

Well, maybe it's better to depend on our version than on the pre-installed one, as it's more predictable (related to #874).

[jwiegley]

@vcunat What do you mean? Rebuild the world using GNU libiconv?

[vcunat]

Yes (that's what we do elsewhere, and we know what version it is without depending on the host).

[jwiegley]

I'd be up for trying it. Where do I make that change?