[OPENMP 4.5] Codegen for 'taskloop' directive.

The taskloop construct specifies that the iterations of one or more associated loops will be executed in parallel using OpenMP tasks. The iterations are distributed across tasks created by the construct and scheduled to be executed.
The next code will be generated for the taskloop directive:
    #pragma omp taskloop num_tasks(N) lastprivate(j)
        for( i=0; i<N*GRAIN*STRIDE-1; i+=STRIDE ) {
          int th = omp_get_thread_num();
          #pragma omp atomic
            counter++;
          #pragma omp atomic
            th_counter[th]++;
          j = i;
    }

Generated code:
task = __kmpc_omp_task_alloc(NULL,gtid,1,sizeof(struct
task),sizeof(struct shar),&task_entry);
psh = task->shareds;
psh->pth_counter = &th_counter;
psh->pcounter = &counter;
psh->pj = &j;
task->lb = 0;
task->ub = N*GRAIN*STRIDE-2;
task->st = STRIDE;
__kmpc_taskloop(
NULL,             // location
gtid,             // gtid
task,             // task structure
1,                // if clause value
&task->lb,        // lower bound
&task->ub,        // upper bound
STRIDE,           // loop increment
0,                // 1 if nogroup specified
2,                // schedule type: 0-none, 1-grainsize, 2-num_tasks
N,                // schedule value (ignored for type 0)
(void*)&__task_dup_entry // tasks duplication routine
);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@267395 91177308-0d34-0410-b5e6-96231b3b80d8