FreeBSD_HEAD_arm64 - Build #3476 - Fixed

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FreeBSD_HEAD_arm64 - Build #3476 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/3476/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/3476/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/3476/console

Change summaries:

302242 by kib:
Fix userspace build after r302235: do not expose bool field of the
structure, change it to int.

The real fix is to sanitize user-visible definitions in sys/event.h,
e.g. the affected struct knlist is of no use for userspace programs.

Reported and tested by:	jkim
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Approved by:	re (gjb)