When the snapshot blob is not aligned properly, loading it can cause a
crash on platforms such as arm.

This was exposed by a SIGBUS/BUS_ADRALN crash on arm when accessing
the blob_data symbol (declared as a byte array) through a reinterpret
cast to uintptr_t in an internal snapshot build.

Thanks to florian.dold@gmail.com for the initial patch.

Bug: v8:9171
Change-Id: I99b071dec3733416f2f01b58a770e30d8f2dcdf2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1582402
Commit-Queue: Dan Elphick <delphick@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61000}