[dev.link] cmd/internal/goobj2: fix comment

Fix a stale comment.

Change-Id: Ic14616310cd8e8703cfc7b1ce50c411be34488fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/238243
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/src/cmd/internal/goobj2/objfile.go b/src/cmd/internal/goobj2/objfile.go
index 7354c21..433eafa 100644
--- a/src/cmd/internal/goobj2/objfile.go
+++ b/src/cmd/internal/goobj2/objfile.go
@@ -139,7 +139,7 @@
 // Package Index.
 const (
 	PkgIdxNone    = (1<<31 - 1) - iota // Non-package symbols
-	PkgIdxBuiltin                      // Predefined symbols // TODO: not used for now, we could use it for compiler-generated symbols like runtime.newobject
+	PkgIdxBuiltin                      // Predefined runtime symbols (ex: runtime.newobject)
 	PkgIdxSelf                         // Symbols defined in the current package
 	PkgIdxInvalid = 0
 	// The index of other referenced packages starts from 1.