Resolve conflicts in favor of the upstream side where possible.
Resolve a logical conflict in archive_windows.h where the upstream
port to Watcom was done slightly differently from ours.
Follow up change from commit ffa6faa4 (libarchive: Include cm_zlib.h to
get zlib used by CMake, 2011-12-20) for new includes of zlib.h in
updated libarchive.