cmd/compile: add MakeTuple generic SSA op to remove duplicate Select[01] rules

cmd/compile: add MakeTuple generic SSA op to remove duplicate Select[01] rules

Change-Id: Id94a5e503f02aa29dc1e334b521770107d4261db
Reviewed-on: https://go-review.googlesource.com/c/go/+/656615
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>