preprocessor: Check for line number overflow Also remove dead code in Tokenizer.l BUG=chromium:668842 Change-Id: Ice18313a64f0bb2242299993bfaa882a6578ad54 Reviewed-on: https://chromium-review.googlesource.com/435042 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>