r367415: can't load linuxulator, link_elf_obj: symbol sdt_provider_linuxulator undefined

[John Kennedy]

  I had this crop up this morning r367410, while yesterdays build against
r367379 seemed fine.  I think this is an issue because of r367395:

	linux(4): Deduplicate unimpl/dummy syscall handlers

  If I tracked it down correctly, the LIN_SDT_PROVIDER_DECLARE(LINUX_DTRACE)
in sys/compat/linux/linux_dummy.c creates an undefined external structure
sdt_provider_linuxulator, which breaks poudriere and X11 (at least via
nvidia drivers).

    [from /var/log/messages]
	kernel: link_elf_obj: symbol sdt_provider_linuxulator undefined
	kernel: linker_load_file: /boot/kernel/linux_common.ko - unsupported file type
	kernel: KLD linprocfs.ko: depends on linux_common - not available or version mismatch

  I guess to be more precise, X11 complained about this:

	(EE) NVIDIA: Failed to initialize the NVIDIA kernel module. Please see the
	(EE) NVIDIA:     system's kernel log for additional error messages and
	(EE) NVIDIA:     consult the NVIDIA README for details.

  Normally no issues there since I have PORTS_MODULES += x11/nvidia-driver,
but I was going to re-poudriere everything since __FreeBSD_version got bumped
and that's when I noticed that poudriere had issues:

	Error: Required kernel module 'linprocfs' not found

  Trying a run against r367420 with the LIN_SDT_PROVIDER_DECLARE() commented out.