No longer have issues with unneeded internal declarations
now that Tokenizer.cpp has been updated so re-enable
compiler warning to catch future issues.
BUG:angleproject:2451
Test: build

Change-Id: I30daadc8c7374bcae753a7e69cb9a72855a1f548
Reviewed-on: https://chromium-review.googlesource.com/1007965
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>