Restore Solaris compatibility fixes lost when internal/x/net/lif moved
to golang.org/x/net/lif. Also fix the Makefile for x/net/lif and
x/net/route.
Change x/sys/cpu to get the cache line size from goarch.sh as the
gofrontend version of internal/cpu does.
Partially based on work by Rainer Orth.
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/194438
From-SVN: r275611