If target cpu is pwr8+, we can generate inlined quadword lock free atomic operations, thus no need to generate libcalls into libatomic.
Instructions needed for inline quadword atomics like lqarx and stqcx are only user-space viable in pwr8 and above. However, pwr6 and pwr7 also feature ppc64.
That change is for the compiler. I am looking for something that makes the libatomic implementation correspondingly lock-free for this type (even if libatomic needs to be deployable on pwr7).