Add DWARF2_LINENO_DEBUGGING_INFO, and use it for nvptx

Add DWARF2_LINENO_DEBUGGING_INFO, and use it for nvptx

	gcc/
	* config/nvptx/nvptx.c (nvptx_option_override): Don't override
	debug options.
	* config/nvptx/nvptx.h (DWARF2_LINENO_DEBUGGING_INFO): Define.
	(DWARF2_DEBUGGING_INFO): Don't define.
	* debug.h (dwarf2_lineno_debug_hooks): Declare.
	* toplev.c (process_options): Add a case for it.
	* dwarf2out.c (dwarf2_lineno_debug_hooks): New variable.
	(dwarf2out_init): Skip most initializations if
	DWARF2_LINENO_DEBUGGING_INFO, but set cur_line_info_table in that
	case.
	* defaults.h (PREFERRED_DEBUGGING_TYPE): Also use DWARF2_DEBUG if
	DWARF2_LINENO_DEBUGGING_INFO.
	* opts.c (set_debug_level): Likewise.

Co-Authored-By: Bernd Schmidt <bernds@codesourcery.com>
From-SVN: r226890