SHM_SHMEM_OPEN probes are buggy

```
if ((fd = shm_open("/shm_open-ohmyohmy", O_CREAT | O_RDWR, 0600)) == -1)
err(1, "shm_open");
```

This should be a SHM_OPEN event, but it shows up as a FILE event because of `O_CREAT`.
We only get a SHM_OPEN event when we `shm_open(2)` an existing thing.

I've worked around it in quark-test but it should be fixed.

Start with the SHM_SHMEM_OPEN probes and reproduce the behavior described in the issue using the shown shm_open call. Compare the emitted event with the quark-test workaround; done means creation with O_CREAT is reported as SHM_OPEN rather than FILE, while existing-object opens retain their expected behavior.

Written by the indexing model from the issue text.