linux(4): Fix loadable modules after r367395

[cem]

Summary

Move dtrace SDT definitions into linux_common module code. Also, build
linux_dummy.c into the linux_common kld -- we don't need separate
versions of these stubs for 32- and 64-bit emulation.

PR: 250897
Reported by: several
X-MFC-With: r367395

Test Plan

Tinderbox i386/amd64/arm64 passes.

Loaded GENERIC in my test VM and loaded all three of linux.ko, linux_common.ko,
and linux64.ko without issue. Ran chrome.

[trasz]

I don't quite understand the problem, nor the fix, but if it works - it works :-)

[cem]

Move MI dummy stubs and SDT definition into linux_common.

[cem]

This tinderboxes and both modules load without issue on amd64. I was able to run a 64-bit binary fine.

[emaste]

No objection if it works

[emaste]

sys/compat/linux/linux_dummy.c

39 ↗

(On Diff #79281)

This comment might be confusing without the context of the removed lines - I would rephrase it to say that we use the same stubs for 32- and 64-bit

[cem]

sys/compat/linux/linux_dummy.c

39 ↗

(On Diff #79281)

I've rewritten this comment somewhat better in what I'll commit, but it's still not especially satisfying. Oh well.