cmd/go: always track visited packages in setPGOProfilePath

cmd/go: always track visited packages in setPGOProfilePath

Currently we only track visited (copied) packages when a copy is
required. When a copy is not required, we will rewalk each package's
entire dependency graph every time we see it, which is terribly
inefficient.

Pull the visited package check up a level so that we visit packages only
once regardless of how many times they are visited.

Fixes #60455.
Fixes #60428.

Change-Id: I4e9b31eeeaa170db650c461a5de2ca984b9aba0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/498735
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>