Makefile.in.in: remove bashisms

Received this from a poor soul 😄 not able to clone [1]

For whatever reasons I can clone - so pass this patch upstream.

BTW - off-topic- is denying of clone a wanted feature or a bug? Have seen other poor souls on xfce mailing list.

However: I think it is worth to pass upstream

[1] https://lists.openembedded.org/g/openembedded-devel/message/88756