FreeBSD_HEAD_arm64 - Build #4164 - Fixed

[jenkins-admin at FreeBSD.org]

FreeBSD_HEAD_arm64 - Build #4164 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/4164/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/4164/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/4164/console

Change summaries:

307909 by andrew:
Import the Cortex String memcpy and memmove into the kernel. On ThunderX
these show a 9-10% reduction in user and system time for a buildworld -j48.

Obtained from:	ABT Systems Ltd
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation

307908 by andrew:
Fix the build on both arm64 and when WITHOUT_FORTH is defined.

 * On arm64 we need to use the ${MACHINE_CPUARCH} subdirectory.
 * env.c is only needed when using forth so only build it there.

Sponsored by:	ABT Systems Ltd

307907 by andrew:
Update the armv6 tlb handling functions to detect if it is running on
hardware that supports the mp extensions. If so it should use the broadcast
tlb invalidate instructions as other CPUs or devices may need to know about
the invalidation.

To simplify the code have the compiler optimise out the else case when not
builing for Cortex-A8.

Sponsored by:	ABT Systems Ltd
Differential Revision:	https://reviews.freebsd.org/D8092