This fixes the bounds checking of "unsigned" numeric literals (those
that do not contains dots) by the parser. In particular this fixes a
bogus truncation to 32-bit in the scanner. It also makes the scanner
more robust by limiting the range of those numeric literals, hence
completely avoiding rounding loss or truncation errors.

R=clemensh@chromium.org
TEST=unittests/AsmJsScannerTest.UnsignedNumbers
BUG=v8:6298

Change-Id: Id31ab3c652e99fa8d3d6663315768e1bfaf3b773
Reviewed-on: https://chromium-review.googlesource.com/486881Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44890}