[m-rev.] for review: put .module_dep and .prof files into grade-specific subdirs

[Zoltan Somogyi]

On Mon, 12 Aug 2024 17:12:35 +1000, Peter Wang <novalazy at gmail.com> wrote:

> On Fri, 02 Aug 2024 12:54:36 +0200 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
>     % mmc -m diff --use-grade-subdirs
>     Making Mercury/int3s/diff.int3
>     ** Error reading file `builtin.m' to generate dependencies.
>     ** Module `builtin' is imported by module `diff'.
>     mercury_compile: cannot find source for module `builtin' in directories `.'
>     mercury_compile: cannot find source for module `builtin' in directories `.'
> 
> We're not installing .module_dep files to grade-specific directories in
> the Mercury install tree.

I will look into this, including fixing that misleading error message.
(If it can't find builtin.module_dep or builtin.m, why does it complain
ONLY about not finding one of them?)

Zoltan.