cmd/go: fix bytes and net the right way

cmd/go: fix bytes and net the right way

Not sure why they used empty.s and all these other
packages were special cased in cmd/go instead.
Add them to the list.

This avoids problems with net .s files being compiled
with gcc in cgo mode and gcc not supporting // comments
on ARM.

Not a problem with bytes, but be consistent.

The last change fixed the ARM build but broke the Windows build.
Maybe *this* will make everyone happy. Sigh.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/144530046