Change some attribute functions to be methods

Change some attribute functions to be methods

This changes most of the attribute-related functions to be methods.
(attr_form_is_block changed in a subsequent patch.)

gdb/ChangeLog
2020-02-08  Tom Tromey  <tom@tromey.com>

	* dwarf2read.c (dwarf2_find_base_address, )
	(read_call_site_scope, rust_containing_type)
	(dwarf2_get_pc_bounds, dwarf2_record_block_ranges)
	(handle_data_member_location, dwarf2_add_member_fn)
	(get_alignment, read_structure_type, process_structure_scope)
	(mark_common_block_symbol_computed, read_common_block)
	(read_tag_string_type, attr_to_dynamic_prop, read_subrange_type)
	(partial_die_info::read, read_attribute_value, new_symbol)
	(lookup_die_type, dwarf2_get_ref_die_offset)
	(dwarf2_get_attr_constant_value, follow_die_ref_or_sig)
	(dwarf2_fetch_die_loc_sect_off, get_DW_AT_signature_type)
	(dwarf2_symbol_mark_computed): Update.
	* dwarf2/attribute.h (struct attribute) <value_as_address,
	form_is_section_offset, form_is_constant, form_is_ref>: Declare
	methods.
	(value_as_address, attr_form_is_section_offset)
	(attr_form_is_constant, attr_form_is_ref): Don't declare.
	* dwarf2/attribute.c (attribute::value_as_address)
	(attribute::form_is_section_offset, attribute::form_is_constant)
	(attribute::form_is_ref): Now methods.

Change-Id: I320dad13002c59b848dc86c39d5d7111c8a15bdc