Use the kernel's sa_restorer for aarch64.

gdb was happy with what we had, but libgcc and libunwind weren't.
libgcc is happy with the kernel's restorer (because of the extra nop),
though libunwind looks like it's going to need code changes regardless.

We could make our restorer more like the kernel's one, but why bother
when we can just let the kernel supply the canonical one?

Bug: 17436734

(cherry picked from commit 1cff9a89645a8f362a9ce19c7f9544e98c1fd9e7)

Change-Id: Ie13d73fd97395e1979a67c2294e036a97c50000d
3 files changed