CHAR_BIT is undefined in certain GCC builds in Linux.

Change-Id: Ib416535614ea5775557eebd7f2dcecb6fdd9340a
Reviewed-on: https://chromium-review.googlesource.com/184397Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>