Re-run mkall.sh on FreeBSD-11.1-RELEASE armv6 for Capsicum consts and
POSIX.1-2008 path relative *at() syscalls.

Add errors_freebsd_arm.go generated semi-automatically using:
https://gist.github.com/paulzhol/c6d54dc2baf2a6bd204b343a15459661
Similar to https://golang.org/cl/51570. In order to handle C enum based
constants that mkerrors.sh missed.

Use fix from https://golang.org/cl/53639 to run Capsicum tests only on amd64.

Fixes golang/go#21136

Change-Id: I9681b033531090e6b1c5e2446a442deb39cf3066
Reviewed-on: https://go-review.googlesource.com/53691Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>