The linux directory contains a config.h generated from Ubuntu 14.04 LTS and
cmake 2.8.12.2.

The mac directory contains a config.h generated from OS X 10.11.6, XCode 7.3,
and cmake 3.4.

The ios directory contains a copy of the mac config.h. Since the mac config.h
contains almost nothing, this is probably fine.

The win directory contains a config.h generated from Windows 7, VS 2013, and
cmake 3.6 with 682f68732898c8ec621427fdd734b3b0ac223ec5 checked out. In a shell
with the VC tools in the path, do:

  cd \src
  git clone https://github.com/google/open-vcdiff
  cd open-vcdiff
  git submodule update --init --recursive
  mkdir buildfoo
  cd buildfoo
  "C:\Program Files\CMake\bin\cmake.exe" -GNinja ..

Then copy the generated config.h out of the root of your open-vcdiff checkout.