There is somes flag errors in the comments, which clarify how to
use pgo for builtin.

Change-Id: I0c418aee57adb7c6774735d32fc63a143bee5c7e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3849654Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Wenqin Yang <wenqin.yang@intel.com>
Cr-Commit-Position: refs/heads/main@{#82650}