Move sym_fns::qf to objfile

Move sym_fns::qf to objfile

Currently the "partial" symbol reader is attached to the objfile's
symbol functions.  However, in order to allow multiple separate
partial symbol readers, this association must be changed.  This patch
moves the "qf" member out of sym_fns as a step toward that goal.

gdb/ChangeLog
2021-03-20  Tom Tromey  <tom@tromey.com>

	* psymtab.c (require_partial_symbols): Check that 'sf' is not
	null.
	* xcoffread.c (xcoff_sym_fns): Update.
	* symfile.h (struct sym_fns) <qf>: Remove.
	* symfile.c (syms_from_objfile_1, reread_symbols): Update.
	* symfile-debug.c (objfile::has_partial_symbols)
	(objfile::find_last_source_symtab)
	(objfile::forget_cached_source_info)
	(objfile::map_symtabs_matching_filename, objfile::lookup_symbol)
	(objfile::print_stats, objfile::dump)
	(objfile::expand_symtabs_for_function)
	(objfile::expand_all_symtabs)
	(objfile::expand_symtabs_with_fullname)
	(objfile::map_matching_symbols)
	(objfile::expand_symtabs_matching)
	(objfile::find_pc_sect_compunit_symtab)
	(objfile::map_symbol_filenames)
	(objfile::find_compunit_symtab_by_address)
	(objfile::lookup_global_symbol_language, debug_sym_fns)
	(install_symfile_debug_logging): Update.
	* objfiles.h (struct objfile) <qf>: New member.
	* mipsread.c (ecoff_sym_fns): Update.
	* machoread.c (macho_sym_fns): Update.
	* elfread.c (elf_sym_fns_gdb_index, elf_sym_fns_debug_names):
	Don't declare.
	(elf_symfile_read, elf_sym_fns, elf_sym_fns_lazy_psyms): Update.
	* dbxread.c (aout_sym_fns): Update.
	* coffread.c (coff_sym_fns): Update.