configure: Replace which(1) with "has" Using "has" is more slick because which(1) is not always there. Signed-off-by: Fam Zheng <famz@redhat.com> Reviewed-by: Stefan Weil <sw@weilnetz.de> Reviewed-by: Amos Kong <akong@redhat.com> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>