Allow libcalls to be installed for legacy __sync optabs.

Allow libcalls to be installed for legacy __sync optabs.

This allows a target which implements the __sync interfaces
in libgcc to continue to use them transparently with the
new __atomic builtins.

It is assumed that these libgcc routines DO NOT use spinlocks.
This is true of all extant libgcc instances.

        * optabs.h (OTI_sync_compare_and_swap, OTI_sync_lock_test_and_set,
        OTI_sync_old_add, OTI_sync_old_sub, OTI_sync_old_ior,
        OTI_sync_old_and, OTI_sync_old_xor, OTI_sync_old_nand,
        OTI_sync_new_add, OTI_sync_new_sub, OTI_sync_new_ior,
        OTI_sync_new_and, OTI_sync_new_xor, OTI_sync_new_nand): Move and
        rename from the direct_optab_index enum.
        (sync_compare_and_swap_optab, sync_lock_test_and_set_optab,
        sync_old_add_optab, sync_old_sub_optab, sync_old_ior_optab,
        sync_old_and_optab, sync_old_xor_optab, sync_old_nand_optab,
        sync_new_add_optab, sync_new_sub_optab, sync_new_ior_optab,
        sync_new_and_optab, sync_new_xor_optab, sync_new_nand_optab): Read
        from the optab_table, not the direct_optab_table.
        (init_sync_libfuncs): Declare.
        (can_compare_and_swap_p): Update parameters.
        * optabs.c (init_sync_libfuncs_1, init_sync_libfuncs): New.
        (can_compare_and_swap_p): Add allow_libcall parameter; if true,
        test for the legacy compare-and-swap libcall.
        (expand_atomic_exchange): Use the legacy test-and-set libcall.
        (expand_atomic_compare_and_swap): Use the legacy CAS libcall.
        (struct atomic_op_functions): Update for optab type changes.
        (maybe_emit_op): Likewise.
        (expand_atomic_fetch_op): Use the legacy fetch-op libcalls.
        * builtins.c (fold_builtin_atomic_always_lock_free): Update call
        to can_compare_and_swap_p.
        * omp-low.c (expand_omp_atomic_fetch_op): Likewise.
        (expand_omp_atomic_pipeline): Likewise.
        * genopinit.c (optabs): Make sync_old_*_optab, sync_new_*_optab,
        sync_compare_and_swap_optab, sync_lock_test_and_set_optab regular
        optabs.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@181134 138bc75d-0d04-0410-961f-82ee72b054a4