We don't track concurrent recompilation/optimization in RCS, disabling it will
give us a better idea of the performance of our compilers.

Change-Id: I8138b09d5f112914f7c7929e9ece6f543423fd03
Reviewed-on: https://chromium-review.googlesource.com/436404Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#42901}