The linux directory contains a config.h generated from a run of configure on
Ubuntu 10.04.1 LTS x86_64, with VCDIFF_USE_BLOCK_COMPARE_WORDS manually
changed to match the $host_cpu test in configure.

The mac directory contains a config.h generated from a run of configure on a
Mac, with VCDIFF_USE_BLOCK_COMPARE_WORDS manually changed to match the
$host_cpu test in configure.