Make gdb.base/a2-run.exp use $inferior_spawn_id and gdb_test_stdio
This one is a little more complicated than the other patches in this
series, because of the exit status wrapper handling, requiring a
little state machine.
gdb/testsuite/ChangeLog:
2015-07-29 Pedro Alves <palves@redhat.com>
* gdb.base/a2-run.exp (saw_usage, saw_exit_wrapper)
(saw_spurious_output): Expect inferior output from
$inferior_spawn_id. Use gdb_test_stdio.