[obish] Convert attach.exp to gdb_test_multiple

[Andrew Cagney]

>>I'll leave committing this to tomorrow (i.e., after the branch date). 
>>> Still passes on amd64 GNU/Linux and PPC NetBSD.
> 
> 
> Hey, we don't have any ppc netbsd results in gdb-testers@.

Nor amd64 GNU/Linux, ppc64 GNU/Linux, ... :-)

> Can I get you to send an abridged gdb.sum file to gdb-testers?
> 
>   grep -v '^PASS:' gdb.sum
>   add a couple lines at the top:
>     netbsd/ppc
>     kernel version number
>     compiler name and version number
>   mail to gdb-testers@

Should there be a gdb/gdb_XXX.sh script that does this, or the 
generation of the file made part of make check?

Andrew