FreeBSD_HEAD_arm64 - Build #4313 - Fixed

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FreeBSD_HEAD_arm64 - Build #4313 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/4313/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/4313/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/4313/console

Change summaries:

309670 by sephe:
hyperv/vmbus: Use pause if possible.

This makes booting on Hyper-V w/ small # of vCPUs work properly.

Reported by:	Hongxiong Xian <v-hoxian microsoft com>, Hongjiang Zhang <honzhan microsoft com>
MFC after:	1 week
Sponsored by:	Microsoft

309669 by gnn:
Fix a kernel panic in DTrace's rw_iswriter subroutine.
On FreeBSD the sense of rw_write_held() and rw_iswriter() were reversed,
probably due to a cut and paste error. Using rw_iswriter() would cause
the kernel to panic.

Reviewed by:	markj
MFC after:	2 weeks
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D8718

309667 by delphij:
Fix typo.