cmd/compile: construct more IR nodes as typed

cmd/compile: construct more IR nodes as typed

As of this CL, all OLITERAL, OLINKSYMOFFSET, ONIL, and OTYPE nodes are
constructed as typed and typechecked.

Change-Id: I39b2ad772a9b0419c701890a505a0949f9ea456e
Reviewed-on: https://go-review.googlesource.com/c/go/+/520795
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>