Don't return DW_AT_name for function name in C++

Don't return DW_AT_name for function name in C++

DW_AT_name for functions typically just contains the base function
name, so lacks namespace, class and parameter information.  It would
be possible to extract all these from the DWARF, but at a considerable
complication of the parser in dwarf2.c, and then you'd need to mangle
it all together.  Much simpler is to look up the actual symbol.  This
patch does that, avoiding the extra symbol lookup when the language
doesn't do name mangling.

	PR 17541
	* dwarf2.c (struct comp_unit): Add "lang".
	(non_mangled): New function.
	(struct funcinfo): Add "is_linkage".  Reorder for better packing.
	Make "name" a const char*.
	(lookup_address_in_function_table): Delete functionname_ptr param.
	(find_abstract_instance_name): Add is_linkage param.  Set if we
	have DW_AT_linkage_name or non_mangled DW_AT_name.
	(scan_unit_for_symbols): Similarly set func->is_linkage.
	(parse_comp_unit): Stash DW_AT_language.
	(comp_unit_find_nearest_line): Replace functionname_ptr param
	with function_ptr param.
	(_bfd_dwarf2_find_nearest_line): Adjust above calls.  Set
	functionname_ptr from function->name.  Call _bfd_elf_find_function
	to retrieve symbol for function if not linkage name.
	(_bfd_elf_find_function): Add bfd_target_elf_flavour test, moved from..
	* elf.c (elf_find_function): ..here.
	(_bfd_elf_find_nearest_line): Adjust calls.
	* elf-bfd.h (_bfd_elf_find_function): Declare.