Marc Poulhies appointed Ada co-maintainer

[Marc Poulhiès]

Hello David,

> I am pleased to announce that the GCC Steering Committee has appointed
> Marc Poulhies as Ada co-maintainer.

Thank you :)

> Marc, please update your listing in the MAINTAINERS file.

I've updated the MAINTAINERS file accordingly in
f4ed610d02aaf8cfcdcb5cf03e0cde65f1f5f890.

Best regards,
Marc