[RFA] testsuite/gdb.base/attach.exp: Add missing kill -9

[Michael Elizabeth Chastain]

[Oops, I sent this to gdb-patches@redhat.com instead of
 gdb-patches@sources.redhat.com]

cv> I'll add it with my next patch (which probably comes today anyway).

Okay.

mec> Also, how did you test this patch?
cv> Erm... that's a funny question.  I tested the testcase by running it.

If you could just say "I ran it on Cygwin" (or whatever you ran it on),
that would be fine.

When some patch breaks, I find it's helpful to know what platform
it actually did work on back when it was submitted.

Michael C