cmd: consolidate "known" os/arch tables into separate package
Common up the the "known OS/Arch" tables from { cmd/go/internal/imports,
cmd/go/internal/modindex, go/build } and relocate them to a new
package, internal/syslist. No change in functionality.
Updates #68606.
Change-Id: I6414a05c96b8fddbdbd9678d322cb49d9b1b0af3
Reviewed-on: https://go-review.googlesource.com/c/go/+/601357 Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>