cmd/link: adjust whitelist for -strictdups checking for plan9

Add a couple of additional entries to the white list used to screen
out errors for builtin functions; these correspond to cases
that appear to come up only on the plan9 builder.

Updates #31503.

Change-Id: I48ab942ab2894240efe651ec7b7eace7aa5cb45e
Reviewed-on: https://go-review.googlesource.com/c/go/+/172986Reviewed-by: David du Colombier <0intro@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/link/internal/objfile/objfile.go

@@ -386,7 +386,9 @@ overwrite:
 			// here is that we get different line numbers on formal
 			// params; I am guessing that the pos is being inherited
 			// from the spot where the wrapper is needed.
-			whitelist := strings.HasPrefix(dup.Name, "go.info.go.interface")
+			whitelist := (strings.HasPrefix(dup.Name, "go.info.go.interface") ||
+				strings.HasPrefix(dup.Name, "go.info.go.builtin") ||
+				strings.HasPrefix(dup.Name, "go.isstmt.go.builtin"))
 			if !whitelist {
 				r.strictDupMsgs++
 			}