AArch64/ARM64: port atomics test to ARM64.

Covers quite a few extra instructions (like any of the max/min ones
which were broken until recently on ARM64).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206575 91177308-0d34-0410-b5e6-96231b3b80d8

Author: TNorthover