The Memory<T>(address) helper requires the address to be aligned. Since
values embedded into ia32/x64 code can in general be unaligned, we must
use ReadUnalignedValue/WriteUnalignedValue to manipulate them.

Bug: v8:3770
Change-Id: I12c3fc6aa09062dcc9188b6782ed4a35e1d684bd
Reviewed-on: https://chromium-review.googlesource.com/c/1436223Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59100}