Replace ia64 S_UNLOCK compiler barrier with a full memory barrier.
_Asm_sched_fence() is just a compiler barrier, not a memory barrier. But
spinlock release on IA64 needs, at the very least, release
semantics. Use a full barrier instead.
This might be the cause for the occasional failures on buildfarm member
anole.
Discussion:
20150629101108.GB17640@alap3.anarazel.de