Change get_objfile_arch to a method on objfile

This changes get_objfile_arch to be a new inline method,
objfile::arch.

To my surprise, this function came up while profiling DWARF psymbol
reading.  Making this change improved performance from 1.986 seconds
to 1.869 seconds.  Both measurements were done by taking the mean of
10 runs on a fixed copy of the gdb executable.

gdb/ChangeLog
2020-04-18  Tom Tromey  <tom@tromey.com>

	* xcoffread.c (enter_line_range, scan_xcoff_symtab): Update.
	* value.c (value_fn_field): Update.
	* valops.c (find_function_in_inferior)
	(value_allocate_space_in_inferior): Update.
	* tui/tui-winsource.c (tui_update_source_windows_with_line):
	Update.
	* tui/tui-source.c (tui_source_window::set_contents): Update.
	* symtab.c (lookup_global_or_static_symbol)
	(find_function_start_sal_1, skip_prologue_sal)
	(print_msymbol_info, find_gnu_ifunc, symbol_arch): Update.
	* symmisc.c (dump_msymbols, dump_symtab_1)
	(maintenance_print_one_line_table): Update.
	* symfile.c (init_entry_point_info, section_is_mapped)
	(list_overlays_command, simple_read_overlay_table)
	(simple_overlay_update_1): Update.
	* stap-probe.c (handle_stap_probe): Update.
	* stabsread.c (dbx_init_float_type, define_symbol)
	(read_one_struct_field, read_enum_type, read_range_type): Update.
	* source.c (info_line_command): Update.
	* python/python.c (gdbpy_source_objfile_script)
	(gdbpy_execute_objfile_script): Update.
	* python/py-type.c (save_objfile_types): Update.
	* python/py-objfile.c (py_free_objfile): Update.
	* python/py-inferior.c (python_new_objfile): Update.
	* psymtab.c (psym_find_pc_sect_compunit_symtab, dump_psymtab)
	(dump_psymtab_addrmap_1, maintenance_info_psymtabs)
	(maintenance_check_psymtabs): Update.
	* printcmd.c (info_address_command): Update.
	* objfiles.h (struct objfile) <arch>: New method, from
	get_objfile_arch.
	(get_objfile_arch): Don't declare.
	* objfiles.c (get_objfile_arch): Remove.
	(filter_overlapping_sections): Update.
	* minsyms.c (msymbol_is_function): Update.
	* mi/mi-symbol-cmds.c (mi_cmd_symbol_list_lines)
	(output_nondebug_symbol): Update.
	* mdebugread.c (parse_symbol, basic_type, parse_partial_symbols)
	(mdebug_expand_psymtab): Update.
	* machoread.c (macho_add_oso_symfile): Update.
	* linux-tdep.c (linux_infcall_mmap, linux_infcall_munmap):
	Update.
	* linux-fork.c (checkpoint_command): Update.
	* linespec.c (convert_linespec_to_sals): Update.
	* jit.c (finalize_symtab): Update.
	* infrun.c (insert_exception_resume_from_probe): Update.
	* ia64-tdep.c (ia64_find_unwind_table): Update.
	* hppa-tdep.c (internalize_unwinds): Update.
	* gdbtypes.c (get_type_arch, init_float_type, objfile_type):
	Update.
	* gcore.c (call_target_sbrk): Update.
	* elfread.c (record_minimal_symbol, elf_symtab_read)
	(elf_rel_plt_read, elf_gnu_ifunc_record_cache)
	(elf_gnu_ifunc_resolve_by_got): Update.
	* dwarf2/read.c (create_addrmap_from_index)
	(create_addrmap_from_aranges, dw2_find_pc_sect_compunit_symtab)
	(read_debug_names_from_section)
	(process_psymtab_comp_unit_reader, add_partial_symbol)
	(add_partial_subprogram, process_full_comp_unit)
	(read_file_scope, read_func_scope, read_lexical_block_scope)
	(read_call_site_scope, dwarf2_ranges_read)
	(dwarf2_record_block_ranges, dwarf2_add_field)
	(mark_common_block_symbol_computed, read_tag_pointer_type)
	(read_tag_string_type, dwarf2_init_float_type)
	(dwarf2_init_complex_target_type, read_base_type)
	(partial_die_info::read, partial_die_info::read)
	(read_attribute_value, dwarf_decode_lines_1, new_symbol)
	(dwarf2_fetch_die_loc_sect_off): Update.
	* dwarf2/loc.c (dwarf2_find_location_expression)
	(class dwarf_evaluate_loc_desc, rw_pieced_value)
	(dwarf2_evaluate_loc_desc_full, dwarf2_locexpr_baton_eval)
	(dwarf2_loc_desc_get_symbol_read_needs)
	(locexpr_describe_location_piece, locexpr_describe_location_1)
	(loclist_describe_location): Update.
	* dwarf2/index-write.c (write_debug_names): Update.
	* dwarf2/frame.c (dwarf2_build_frame_info): Update.
	* dtrace-probe.c (dtrace_process_dof): Update.
	* dbxread.c (read_dbx_symtab, dbx_end_psymtab)
	(process_one_symbol): Update.
	* ctfread.c (ctf_init_float_type, read_base_type): Update.
	* coffread.c (coff_symtab_read, enter_linenos, decode_base_type)
	(coff_read_enum_type): Update.
	* cli/cli-cmds.c (edit_command, list_command): Update.
	* buildsym.c (buildsym_compunit::finish_block_internal): Update.
	* breakpoint.c (create_overlay_event_breakpoint)
	(create_longjmp_master_breakpoint)
	(create_std_terminate_master_breakpoint)
	(create_exception_master_breakpoint, get_sal_arch): Update.
	* block.c (block_gdbarch): Update.
	* annotate.c (annotate_source_line): Update.

gdb/linux-tdep.c

@@ -2326,7 +2326,7 @@ linux_infcall_mmap (CORE_ADDR size, unsigned prot)
      "mmap" uses 64-bit off_t on x86_64 and 32-bit off_t on i386 and x32.  */
   struct value *mmap_val = find_function_in_inferior ("mmap64", &objf);
   struct value *addr_val;
-  struct gdbarch *gdbarch = get_objfile_arch (objf);
+  struct gdbarch *gdbarch = objf->arch ();
   CORE_ADDR retval;
   enum
     {
@@ -2365,7 +2365,7 @@ linux_infcall_munmap (CORE_ADDR addr, CORE_ADDR size)
   struct objfile *objf;
   struct value *munmap_val = find_function_in_inferior ("munmap", &objf);
   struct value *retval_val;
-  struct gdbarch *gdbarch = get_objfile_arch (objf);
+  struct gdbarch *gdbarch = objf->arch ();
   LONGEST retval;
   enum
     {