I updated some references to 6g, 6l and friends that I came across, as those
programs don't exist anymore. I also fixed some echos in make.rc to match other make.* scripts while I was there.

Change-Id: Ib84532cd4688cf65174dd9869e5d42af98a20a48
Reviewed-on: https://go-review.googlesource.com/11162Reviewed-by: Ian Lance Taylor <iant@golang.org>