This adds a new target :generated_cc_files which generates all
generated .cc files and is quick to build (~5sec on my machine).

TBR=yangguo@chromium.org

Change-Id: I51485635671b55302b06f1ea300e86ef1745931e
Bug: v8:8526
Reviewed-on: https://chromium-review.googlesource.com/c/1354881
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57941}