* sysdeps/sparc/sparc32/sparcv9/bits/atomic.h
(__arch_compare_and_exchange_val_32_acq): Use %g0 as second
argument of CAS if possible.
* sysdeps/sparc/sparc64/bits/atomic.h
(__arch_compare_and_exchange_val_32_acq): Likewise.
(__arch_compare_and_exchange_val_64_acq): Likewise.