shells/antibody: Unbreak on aarch64

> Building antibody from .

golang.org/x/sys/unix

vendor/golang.org/x/sys/unix/cap_freebsd.go:18:23: undefined: CAP_RIGHTS_VERSION_00
vendor/golang.org/x/sys/unix/cap_freebsd.go:19:23: undefined: CAP_RIGHTS_VERSION_00
vendor/golang.org/x/sys/unix/cap_freebsd.go:46:21: undefined: CapRights
vendor/golang.org/x/sys/unix/cap_freebsd.go:50:24: undefined: CapRights
vendor/golang.org/x/sys/unix/cap_freebsd.go:55:27: undefined: CapRights
vendor/golang.org/x/sys/unix/cap_freebsd.go:90:29: undefined: CapRights
vendor/golang.org/x/sys/unix/syscall_unix_gc.go:12:6: missing function body
vendor/golang.org/x/sys/unix/syscall_unix_gc.go:13:6: missing function body
vendor/golang.org/x/sys/unix/syscall_unix_gc.go:14:6: missing function body
vendor/golang.org/x/sys/unix/syscall_unix_gc.go:15:6: missing function body

http://thunderx1.nyi.freebsd.org/data/head-arm64-default/p518178_s355024/logs/errors/antibody-4.2.0_1.log

Unbreak by updating golang.org/x/sys to 33540a1f6037 which adds support for
freebsd/arm64.

PR: 242446
Approved by: adamw (maintainer)