cmd/compile: switch to typed aux in more amd64 rules
    
    Passes
    
      gotip build -toolexec 'toolstash -cmp' -a std
    
    Change-Id: I9acda12d24f85d0b12d0cbbedbf9df3b4afcb31b
    Reviewed-on: https://go-review.googlesource.com/c/go/+/256099
    Trust: Alberto Donizetti <alb.donizetti@gmail.com>
    Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
    TryBot-Result: Go Bot <gobot@golang.org>
    Reviewed-by: Keith Randall <khr@golang.org>