On FreeBSD x86_64 is named amd64

Change-Id: I14c653f8b3fe0dc9855aa51643cfc40cbccb763e
Reviewed-on: https://gerrit.libreoffice.org/9714
Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>