Make Makefile argument optional for easier use from tools.

[michael-delarue-axomic]

This seems to solve problems with running checkmake from pre-commit. It very simply makes the Makefile argument optional which means that checkmake doesn't seem to run.
(see also #80 and some comments on other (closed) issues (e.g. #69)

Checklist

Not all of these might apply to your change but the more you are able to check
the easier it will be to get your contribution merged.

• [x ] CI passes
• [x ] Description of proposed change
• [x ] Documentation (README, docs/, man pages) is updated
• [x ] Existing issue is referenced if there is one
• [!! ] Unit tests for the proposed change

no unit test yet since this basically does nothing. Might investigate learning how to do that if considered worthwhile.

[michael-delarue-axomic]

According to the pre-commit documentation for adding new hooks the default is not to run hooks when there are no files to be checked and the checkmake hook configuration does not override this, so I am not really sure why this is helping, but it has.

[colindean]

Can you show the output you're seeing when it fails? I've used checkmake at rev c047d51 for many months now without a problem across more than a dozen repos.

[mrtazz]

it would be good to have a more detailed description here of what exactly fails and how this is fixing it. Especially since there are reports where things are working.