[og9] Remove duplicate SESE code in NVPTX backend

[og9] Remove duplicate SESE code in NVPTX backend

	gcc/
	* config/nvptx/nvptx.c (omp-sese.h): Include.
	(bb_pair_t, bb_pair_vec_t, pseudo_node_t, bracket, bracket_vec_t,
	bb_sese, bb_sese::~bb_sese, bb_sese::append, bb_sese::remove,
	BB_SET_SESE, BB_GET_SESE, nvptx_sese_number, nvptx_sese_pseudo,
	nvptx_sese_color, nvptx_find_sese): Remove.
	(nvptx_neuter_pars): Call omp_find_sese instead of nvptx_find_sese.
	* omp-sese.c (omp-sese.h): Include.
	(struct parallel): Rename to...
	(struct parallel_g): This.
	(parallel::parallel, parallel::~parallel): Rename to...
	(parallel_g::parallel_g, parallel_g::~parallel_g): These.
	(omp_sese_dump_pars, omp_sese_find_par, omp_sese_discover_pars,
	populate_single_mode_bitmaps, find_ssa_names_to_propagate,
	find_partitioned_var_uses, find_local_vars_to_propagate,
	neuter_worker_single): Update for parallel_g name change.
	(bb_pair_t, bb_pair_vec_t): Remove.
	(omp_find_sese): Make global.
	* omp-sese.h (bb_pair_t, bb_pair_vec_t): New.
	(omp_find_sese): Add prototype.

(cherry picked from openacc-gcc-9-branch commit
2656f9aa1b7e922ccf2d2af9c978e130681643ee)