gnuplot: fix build on darwin

gnuplot: fix build on darwin

This was a crazy tangle of dependencies.

I didn't end up using `wxGTK29`, but I left the fixes in here for others who
wish to use it.

In order to get `gnuplot` building on darwin, I had to do the following:

* `cracklib`: add `libintlOrEmpty` to build inputs
* `emacs24`: build with gccApple (fixes http://hydra.nixos.org/build/5440806)
* `glib`: remove unnecessary restrictions
* `gnome.GConf`: disable `polkit` (requires `pam` which requires `shadow.h`
  which is not available on darwin), add --enable-static to configureFlags
* `gnome.ORBit2`: add `libintlOrEmpty` to build inputs
* `gnuplot`: add `readline` to build inputs, don't use wxGTK (gives a malloc
  double free error)
* `gobject-introspection`: add `libintlOrEmpty` to build inputs, add `otool` as
  build input
* `gst-plugins-base`: remove `alsaLib` and `cdparanoia` from build inputs when
  building on darwin, add `cairo` to build inputs
* `liboil`: force architecture to x86_64
* `llvm`: add `DYLD_LIBRARY_PATH` (recent modifications broke the build on
  darwin -- fixes http://hydra.nixos.org/build/5407837), don't build with shared
  libs
* `otool`: add expression (this is just copied straight from /usr/bin -- I'm
  open to suggestions on how to improve)
* `setFile`: add expression (same as for `otool` -- straight from /usr/bin)
* `wxGTK29`: use `clang` for Objective-C++ compiler, add configure flags to
  enable building on 64-bit, add `setFile` to build inputs