Resubmit with clang build issue fixed. The result of a short-circuited
operation is now either 0 or 1.

ESSL 3.00 spec section 3.4 mentions that the second operand in a logical
&& or || preprocessor operation is evaluated only if the first operand
doesn't short-circuit the expression. The non-evaluated part of a
preprocessor expression may also have undefined identifiers.

Make the expression parser follow the spec by ignoring errors that are
generated inside short-circuited expressions. This includes undefined
identifiers and divide by zero.

BUG=angleproject:347
TEST=dEQP-GLES3.functional.shaders.preprocessor.undefined_identifiers.*
     angle_unittests

Change-Id: I4163f96ec46d40ac859ffb39d91b89490041e44d
Reviewed-on: https://chromium-review.googlesource.com/297252Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>