Also teach MSVC that ANGLE_CRASH() can't return.

Also fix instances of the warning in build configurations where
UNREACHABLE() can return (e.g. release without dcheck_always_on
or debug).

If the UNREACHABLE()s are truly unreachable, this change has
no behavior change.

Bug:  chromium:810767

Change-Id: I68f3587cf3e268c3ef634dce7ae3d70399859d0f
Reviewed-on: https://chromium-review.googlesource.com/914842Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>