sparc: Convert to atomic_exchange.

sparc: Convert to atomic_exchange.

        * config/sparc/sync.md (I124MODE): New mode iterator.
        (memory_barrier): Remove.
        (atomic_exchangesi): New.
        (swapsi): Rename from *swapsi.
        (atomic_test_and_set<I124MODE>): New.
        (ldstubqi): Rename from *ldstubqi, merge with expander.
        (ldstub<I24MODE>): Rename from *ldstub<I24MODE>, merge with expander.
        (sync_lock_test_and_setsi): Remove.
        (sync_lock_test_and_set<I12MODE>): Remove.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@181852 138bc75d-0d04-0410-961f-82ee72b054a4