We only support Sparc V9 and better as V8 lacks an atomic CAS instruction
which we need for SMP. This means that we have to pass -mcpu=v9 to GCC when
compiling and assembling. Hardcoding the flag is hackish but seems to be
our best bet at the moment. It can still be overridden by the user as GCC
picks the best -mcpu flag regardless of the ordering.