[m-rev.] for post-commit review: Ensure trans_opt_deps rules can be read back.

[Julien Fischer]

On Thu, 15 Dec 2022, Peter Wang wrote:

> When writing out a trans_opt_deps rule in a .d file,
> always write each dependency on a separate line. If the rule is
> written "horizontally" because there is only one dependency, e.g.
>
>    foo.trans_opt_date : bar.trans_opt
>
> then maybe_read_d_file_for_trans_opt_deps will not be able to parse the
> list, and the .trans_opt file will not be used.
>
> compiler/mmakefiles.m:
>    As above.

Good catch, that's a pernicious little problem.
(This one will need to go on to the release branch as well.)

Julien.