OpenACC 1.0 support -- GENERIC nodes and gimplify stubs.

     gcc/
     * gimplify.c (is_gimple_stmt): Stub OpenACC directives and clauses.
     (gimplify_scan_omp_clauses, gimplify_adjust_omp_clauses): Likewise.
     (gimplify_expr): Likewise.
     * omp-low.c (scan_sharing_clauses): Likewise.
     (gimple_code_is_oacc): New helper function.
     (scan_sharing_clauses): Use it.
     * tree-core.h
     (OMP_CLAUSE_ASYNC, OMP_CLAUSE_NUM_GANGS, OMP_CLAUSE_NUM_WORKERS,
     OMP_CLAUSE_VECTOR_LENGTH, OMP_CLAUSE_GANG, OMP_CLAUSE_WORKER,
     OMP_CLAUSE_VECTOR, OMP_CLAUSE_INDEPENDENT,
     OMP_CLAUSE_USE_DEVICE, OMP_CLAUSE_HOST, OMP_CLAUSE_DEVICE_RESIDENT,
     OMP_CLAUSE_OACC_DEVICE, OMP_CLAUSE_DEFAULT, OMP_CLAUSE_WAIT): New 
clauses.
     * tree-pretty-print.c (dump_omp_clause): Print OpenACC clause.
     (dump_generic_node): Print OpenACC directives and its clauses.
     * tree.c (omp_clause_num_ops): Add OpenACC clauses.
     (omp_clause_code_name): Likewise.
     (walk_tree_1): Likewise.
     * tree.def (OACC_KERNELS): New tree node.
     (OACC_DATA, OACC_HOST_DATA, OACC_DECLARE, OACC_UPDATE): Likewise.
     (OACC_ENTER_DATA, OACC_EXIT_DATA, OACC_WAIT, OACC_CACHE): Likewise.
     * tree.h (OACC_BODY): New macros.
     (OACC_KERNELS_BODY, OACC_KERNELS_CLAUSES, OACC_CLAUSE_NUM_GANGS_EXPR,
     OMP_CLAUSE_NUM_WORKERS_EXPR, OMP_CLAUSE_VECTOR_LENGTH_EXPR,
     OMP_CLAUSE_VECTOR_EXPR, OMP_CLAUSE_WORKER_EXPR, OMP_CLAUSE_GANG_EXPR,
     OMP_CLAUSE_ASYNC_EXPR,
     OMP_WAIT_EXPR, OACC_DATA_BODY, OACC_DATA_CLAUSES, 
OACC_DECLARE_CLAUSES,
     OACC_UPDATE_CLAUSES, OACC_WAIT_CLAUSES, OACC_CACHE_CLAUSES,
     OACC_HOST_DATA_BODY, OACC_HOST_DATA_CLAUSES): Likewise.