The newly introduced --rcs-cpu-time flag enables CPU time for all
runtime call stats timers. By default we still keep on using good
old wall time.

This CL also adds the long-awaited --rcs short flag.

Change-Id: I3173e3a0f846ec3bf0d319624a37741c56914be5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2060304Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66427}