Illegal instructions

[Robert Swindells <rjs%fdy2.co.uk@localhost>]

On my Pinebook I rebuilt the kernel with sigill_debug = 1 to see what
was going on with older arm binaries.

I'm seeing regular console messages like this from running the standard
aarch64 binaries:

TRAP: pid 197 (syslogd), uid 0: Unknown Reason (Illegal Instruction): esr=0x2000000: pc=0xfffffbc9e9d0: sha512su0 v0.2d, v0.2d

The address and instruction are always the same, different programs
(cron, login, pkg_info, syslogd).