gdb/m2: add builtin procedure function ADR

This patch introduces ADR to the Modula-2 language interface.
It return the address of the parameter supplied.
The patch also contains a dejagnu test for ADR.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>
Reviewed-By: Eli Zaretskii <eliz@gnu.org>