[m-rev.] for review: fix bug #196: binary compatiblity checks in C grade don't work

[Zoltan Somogyi]

On Fri, 15 Jul 2016 01:16:25 +1000 (AEST), Julien Fischer <jfischer at opturion.com> wrote:
> Is anyone intending to review this one?  In the absence of any comments
> I'll commit it later today.

I thought I already reviewed the idea, and said that I would prefer
to fix the problem by exporting a function that refers to the value
of MR_GRADE_VAR. I think this would be more robust in the face
of compiler optimizations, though it does have the slight downside
of adding one symbol per module to the executable's symbol table.

Zoltan.