We currently try to compile more deterministically in single threaded
mode, which unexpectedly degrades performance due to repeated publishing
of single compilation units. We should only pay this cost in predictable
mode.

R=clemensb@chromium.org

Change-Id: I7eb06a0849d3001b99d057adec9850810a1d6a63
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2218288Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68067}