[M70] Cherry pick a memory alignment issue on ARM

https://unicode-org.atlassian.net/browse/ICU-20001

We have exactly the same fix already in 69 branch for
another class. See crbug.com/865100 .

TBR=ftang@chromium.org

Bug: 896322
Test: See bug comment 21
Change-Id: I8aed41a29ed7382ea19ac90825d3440f58372247
Reviewed-on: https://chromium-review.googlesource.com/c/1293071
Reviewed-by: Jungshik Shin <jshin@chromium.org>
3 files changed