Add Ada test case with long array indices

Add Ada test case with long array indices

This patch adds a test case to test that the previous two patches did
their job.

With the current gdb, this test fails:

    (gdb) print some_regular_access.all
    Value out of range.

The bug here is that the array has an index type that is wider than
'int', which is perfectly acceptable in Ada.

Note that this series doesn't quite go far enough: in Ada the index
could be a 128-bit integer.  This change would be more invasive; and
in practice this doesn't really seem to come up much -- so I've
deferred it.