[m-dev.] move to // comments in C

[Julien Fischer]

Hi Zoltan,

On Sat, 9 Jul 2016, Zoltan Somogyi wrote:

> As I was cleaning up the runtime, I noticed that it had one // style
> comment, in mercury_stack_trace.c, which has been there since 2012.
> Since noone has reported any problems with it, I propose that we
> change our official programming style for C code to prefer // comments
> over /* */ comments.

No objection from me.  (The only place where C99 potentially causes
problems is MSVC, but it has supported // style comments as an
extension for a long time.)

Julien.