[Ada] new "-margs" flag to gnatmake

[guerby@acm.org]

> There's a proposal for these kind of scripts which should address
> this problem, and it even avoids cluttering the PATH, see
> http://cert.uni-stuttgart.de/projects/ada/gnae.php .

I still thinks -margs is a useful addition, irrespective of various
existing specification proposals :). It allows configuration tools to
rely on gnatmake knowledge of what to do with various flags instead of
duplicating this knowledge everywhere.

-- 
Laurent Guerby <guerby@acm.org>