There is no jumbo_executable target atm, so split the cctest v8_executable
target into cctest and cctest_sources.

Bug: chromium:746958
Change-Id: Iec0956234d026039c4d29921170dd2f0955222ca
Reviewed-on: https://chromium-review.googlesource.com/680575Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Mostyn Bramley-Moore <mostynb@opera.com>
Cr-Commit-Position: refs/heads/master@{#48147}