Add rtx_jump_table_data::get_labels method

Add rtx_jump_table_data::get_labels method

gcc/
	* rtl.h (rtx_jump_table_data::get_labels): New method.
	* cfgbuild.c (make_edges): Replace hand-coded lookup of labels
	with use of the new rtx_jump_table_data::get_labels method.
	(purge_dead_tablejump_edges): Strengthen param "table" from rtx
	to rtx_jump_table_data *.  Simplify by using get_labels method.
	* cfgrtl.c (delete_insn): Replace use of JUMP_TABLE_DATA_P with
	a dyn_cast, introducing local "table", using it to replace
	label-lookup logic with a get_labels method call.
	(patch_jump_insn): Simplify using get_labels method.
	* dwarf2cfi.c (create_trace_edges): Likewise.
	* rtlanal.c (label_is_jump_target_p): Likewise.

From-SVN: r214476