This CL introduces R_ADDRARM64, which is similar to R_ADDRPOWER.

Fixes #10112.

Change-Id: I309e3df7608b9eef9339196fdc50dedf5f9439f1
Reviewed-on: https://go-review.googlesource.com/8438Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>
Reviewed-by: David Crawshaw <crawshaw@golang.org>