Cherry pick "Avoid crash on some 64b ARM NEON platforms."

Bug: 18297786

Original Description:

Avoid crash on some 64b ARM NEON platforms.

The compiler may choose to use x30 for a local loop counter;
ensure it's saved. Patch from kevin.petit@arm.com,
verified by benm@google.com.

R=djsollen@google.com

Committed:
https://skia.googlesource.com/skia/+/414867c00463e1405ce2234cf7591b1788d20b9f

Change-Id: Ib1c4b33a1cf9b957b01684470e9d719b730b31be
1 file changed