In this case it will work for any make commangs. For example:
make COMPAT_TEST=y -C test/zdtm/lib

travis-ci: success for zdtm: handle COMPAT_TEST from Makefile.inc
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>