[OPENMP] Fix for '#pragma omp task' codegen.

Internal task structure must be generated like
typedef struct kmp_task {
  void *              shareds;
  kmp_routine_entry_t routine;
  kmp_int32           part_id;
  kmp_routine_entry_t destructors;
} kmp_task_t;

struct kmp_task_t_with_privates {
  kmp_task_t task_data;
  .kmp_private. privates;
};
to avoid possible additional alignment bytes in first fields (shareds, routine, part_id and destructors). Runtime library is not aware of such kind additional alignment bytes.

llvm-svn: 237561