cmd/compile: refactor Escape.tagHole

cmd/compile: refactor Escape.tagHole

This CL refactors tagHole to handle all three call situations (unknown
function; known function in same analysis batch; known function in
previous analysis batch). This will make it somewhat easier to reuse
in a followup CL.

Passes toolstash-check.

Change-Id: I764d047a333dfc593d721a881361683e94b485df
Reviewed-on: https://go-review.googlesource.com/c/go/+/229059
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>