[test] Upgrade gcmole plugin

This upgrades to a precompiled plugin version including:
https://chromium.googlesource.com/v8/v8/+/4b0edcf7

BUG=v8:5970
TBR=clemensh@chromium.org,mstarzinger@chromium.org

Change-Id: I28ecdd568e4bc075533b3d14b7946a4a7ce5f9e0
Reviewed-on: https://chromium-review.googlesource.com/443648
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43255}

tools/gcmole/gcmole-tools.tar.gz.sha1

-b10748117f8f53d05dda0a77424b8794e645e330
+a21e6b0d08afcfe454042c2c1fbf1d1738caf129
\ No newline at end of file