The command: `make check-tabs` fails on Windows due to line ending conversions
caused by the following setting: `git config --global core.autocrlf true`
(the whitelist `build-aux/initial-tab-whitelist` becomes a blacklist)
This patch adds a .gittatribute file to build-aux to force LF endings
on Windows.
Signed-off-by: Alin Gabriel Serdean <aserdean@ovn.org> Co-authored-by: Aaron Conole <aconole@redhat.com> Signed-off-by: Aaron Conole <aconole@redhat.com> Acked-by: Ben Pfaff <blp@ovn.org>