FreeBSD_HEAD_arm64 - Build #3716 - Fixed

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FreeBSD_HEAD_arm64 - Build #3716 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/3716/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/3716/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/3716/console

Change summaries:

303437 by mav:
Fix r303429 build with invariants.

303436 by ed:
Regenerate system call table for r303435.

303435 by ed:
Change the return type of msgrcv() to ssize_t as required by POSIX.

It looks like the msgrcv() system call is already written in such a way
that the size is internally computed as a size_t and written into all of
td_retval[0]. This means that it is effectively already returning
ssize_t. It's just that the userspace prototype doesn't match up.