[m-rev.] for review: Fix mmake issue when compiling without a bootstrap compiler.

[Julien Fischer]

On Wed, 18 Oct 2023, Peter Wang wrote:

> Fix an issue exposed by commit 7d001786a0d2b26a1cc6195fd63bd05b9843be03.
>
> VPATH indirectly refers to GRADESTRING_NO_TARGET.
> When the VPATH is being calculated after the makefile is read,
> the reference to GRADESTRING_NO_TARGET causes make to try to run the
> Mercury compiler to output a grade string, but we may not yet have a
> working Mercury compiler.
>
> scripts/Mmake.vars.in:
>    Set EXTRA_INIT_DIRS_NO_TARGET to a non-empty string
>    (that references GRADESTRING_NO_TARGET in a pattern substitution)
>    only if EXTRA_LIB_DIRS is actually non-empty.

I think that will work; I suggest you commit it and we can see what
effect it has on today's ROTD.

Julien.