bootstrap: use glibtoolize on MacOS * build-aux/bootstrap (check_versions): Convert libtool into libtoolize. (tool search): Move libtool check earlier, and look for glibtoolize for MacOS. (gnulib_tool_options): Auto-add --libtool when appropriate. Reported by Justin Clift. Signed-off-by: Eric Blake <eblake@redhat.com>