Change libvixl symbol visibility. am: 07f3653da4 am: 6d0be08f95 am: 4632b10c27

Original change: https://android-review.googlesource.com/c/platform/external/vixl/+/1697237

Change-Id: I593c20dde4d5893a17e13f42a3f432d54ffcd909