[RFA] Fix logic error suppressing attach.exp tests

[Michael Snyder]

Fred Fish wrote:
> 
> > I don't have approval authority in testsuite/gdb.base but I like this patch.
> > Can anyone test it on more targets and hosts?
> 
> I've not gotten any explicit approval for this patch yet.  It seems
> like a pretty obvious fix.  I'm tempted to just check it in under the
> "obvious typo fix" rule.

Oh, heck, I'll put on my "mighty universal check-in" hat and give you
approval.
;-)

Michael