[m-rev.] for review: support MS VC 2015

[Julien Fischer]

Hi Sebastian,

On Tue, 1 Mar 2016, Sebastian Godelet wrote:

> Support compiling Mercury with MS Visual C compiler 2015, which currently fails configuring.
> This is due to the added support of the ISO C99 (v)snprintf function family which then fails the functional test.
> Instead of issuing a warning in the AC_CHECK_FUNC test, `cl' exists with #error, thus failing the test.

What exactly is the error you are seeing?  (I'm not objecting to the
change; I just want to understand what's going on.)

Julien.