linux: handle split resume requests with target-async off

linux: handle split resume requests with target-async off

With

    target-async off
    scheduler-locking off
    schedule-multiple on

and

    record btrace

the record-btrace target splits resume and stop requests when there are
multiple inferiors and some are replaying while others are recording.

Since wait would be blocking in this configuration, we cannot afford to
split wait requests, as well, or risk a hang.

This leads to scenarios where the target beneath record-btrace received

    resume requests for inferiors other than the current inferior, since
    that would be handled by the record target above.

    stop requests, but has not gotten the chance to wait for the
    corresponding event before receiving another resume request.

Handle those cases for the linux native target.