[PATCH] gdb.base/setshow.exp: fix racy tests (PR testsuite/12649)

[Tom Tromey]

>>>>> "Marek" == Marek Polacek <mpolacek@redhat.com> writes:

Marek> Yes, this works.  Thank you, Andreas!
Marek> Tom, ok to apply with these changes?  Thanks,

Yes, thanks.

Tom