Fix ff8b1abb

This fixes the problem with the alignment of typed arrays in turbofan. Namely,
Float64 typed arrays weren't properly aligned on 32bit architectures,
and this causes crashes on those architectures that do not support misaligned
memory access.

TEST=mjsunit/es6/typedarray-*
BUG=v8:6075

Review-Url: https://codereview.chromium.org/2784253002
Cr-Commit-Position: refs/heads/master@{#44366}