[m-rev.] for review: simplify the use of mdbrc by test cases

[Julien Fischer]

On Tue, 26 Oct 2021, Peter Wang wrote:

>>> Maybe we should delete the .DEFAULT target in the Makefile.
>>
>> It does seem a bit pointless given that just invoking "make"
>> without the default target will invoke the "all" target anyway.
>
> I meant this:
>
>    .DEFAULT:
> 	    $(MMAKE) $@

Yes, I know you meant that -- however, I missed the fact that
it was MMAKE rather than MAKE.

> It allows you to build targets that are only listed in the Mmakefile
> using plain "make" instead of "mmake". If we delete that rule, we can
> say that the only targets we support with plain "make" are those in the
> Makefile, and no more.

I can't think of a time when I've invoked one of the mmake targets using
plain make.  I think we can delete it and then document that the
supported targets are the ones listed in the Makefile.

Julien.