Don't use byte-width instructions when accessing |compiler_hints|
field (only FunctionKind bit field accesses are yet to be fixed).
This CL eases adding new bit fields to the compiler hints field.

Bug: v8:6470
Change-Id: Ibc2dfb42c0bf0df49fcb9e37c10fda789db4c3c8
Reviewed-on: https://chromium-review.googlesource.com/528120Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45844}