Improve the performance of gcmole by

  * Precompiling the regexes in GCSuspectsCollector.Resolve
  * Merging those regexes into a single regex, using '|'
  * Changing multiprocess clang plugin invocation to threaded (running
    the plugin releases the GIL so this can efficiently thread). This
    uses a simple worker pool with a single work queue.
  * Change clang plugin invocation loop to yield after each invocation.
    This pipelines the dump-callees plugin and GCSuspectsCollector
    Parse/Resolve, so that the parse can happen while waiting for other
    callee dumps to finish.

Change-Id: Ib9fca70dbcfd2f9d1aebc8bd11aa1d1f7d34e24a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2562242Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71617}