Add line debug info for virtual thunks

There is no debug info when the DECL_IGNORED_P flag
is set.  But sometimes we have the line info of the
function decl, as in the case of on virtual thunks.
So instead of no line info at all, we emit at least
the location of the function decl.
On the other side, there are DECL_IGNORED_P functions
which do not have any source line info at all.
Remove those from the debug_range info, to make it
clear for the debugger that the line info for these
functions is invalid.  This has the effect that the
debugger will not step into the function without
debug info.

2021-05-06  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	PR ipa/97937
	* debug.h (gcc_debug_hooks): Add set_ignored_loc function pointer.
	* dwarf2out.h (dw_fde_node::ignored_debug): New data item.
	* dbxout.c (dbx_debug_hooks, xcoff_debug_hooks): Add dummy
	set_ignored_loc callbacks.
	* debug.c (do_nothing_debug_hooks): Likewise.
	* vmsdbgout.c (vmsdbg_debug_hooks): Likewise.
	* dwarf2out.c (text_section_used, cold_text_section_used): Remove.
	(in_text_section_p, last_text_label, last_cold_label,
	switch_text_ranges, switch_cold_ranges): New data items.
	(dwarf2out_note_section_used): Remove.
	(dwarf2out_begin_prologue): Set fde->ignored_debug and
	in_text_section_p.
	(mark_ignored_debug_section): New helper function.
	(dwarf2out_end_epilogue, dwarf2out_switch_text_section): Call
	mark_ignored_debug_section.
	(dwarf2_debug_hooks): Use dwarf2out_set_ignored_loc.
	(dwarf2_lineno_debug_hooks): Use dummy for set_ignored_loc.
	(size_of_aranges): Adjust formula for multi-part text ranges size.
	(output_aranges): Output multi-part text ranges.
	(dwarf2out_set_ignored_loc): New callback function.
	(dwarf2out_finish): Output multi-part text ranges.
	(dwarf2out_c_finalize): Clear new data items.
	* final.c (final_start_function_1): Call set_ignored_loc callback.
	(final_scan_insn_1): Likewise.
	* ggc-page.c (gt_ggc_mx): New helper function.
	* stringpool.c (gt_pch_nx): Likewise.