mach-o: layout executables

bfd/
	* mach-o.h (bfd_mach_o_dyld_info_command): Add rebase_content,
	bind_content, weak_bind_content, lazy_bind_content,
	export_content.
	(bfd_mach_o_load_command): Add comments, add next field.
	(mach_o_data_struct): Replace commands field by first_command
	and last_command.
	* mach-o.c (bfd_mach_o_append_command): New function.
	(bfd_mach_o_bfd_copy_private_symbol_data): Add blank lines.
	(bfd_mach_o_bfd_copy_private_section_data): Check flavour,
	copy fields.
	(bfd_mach_o_bfd_copy_private_header_data): Copy load commands.
	(bfd_mach_o_pad4, bfd_mach_o_pad_command): New functions.
	(bfd_mach_o_write_thread): Use macro instead of literal.
	(bfd_mach_o_write_dylinker, bfd_mach_o_write_dylib)
	(bfd_mach_o_write_main, bfd_mach_o_write_dyld_info): New
	functions.
	(bfd_mach_o_write_symtab_content): New function (extracted
	from bfd_mach_o_write_symtab).
	(bfd_mach_o_write_symtab): Split.
	(bfd_mach_o_count_indirect_symbols): Move
	(bfd_mach_o_build_dysymtab): Remove layout code.
	(bfd_mach_o_write_contents): Rewritten to build commands in order.
	(bfd_mach_o_count_sections_for_seg): Remove.
	(bfd_mach_o_build_obj_seg_command): New function (extracted from
	bfd_mach_o_build_seg_command).
	(bfd_mach_o_build_exec_seg_command): New function.
	(bfd_mach_o_build_dysymtab_command): Remove.
	(bfd_mach_o_layout_commands): New function.
	(bfd_mach_o_init_segment): New function.
	(bfd_mach_o_build_commands): Major rework to handle non-object
	files.
	(bfd_mach_o_alloc_and_read, bfd_mach_o_read_dyld_content): New
	function.
	(bfd_mach_o_read_dyld_info): Clear content fields.
	(bfd_mach_o_read_segment): Adjust call.
	(bfd_mach_o_flatten_sections): Adjust as now load commands are
	chained.
	(bfd_mach_o_scan_start_address, bfd_mach_o_scan)
	(bfd_mach_o_mkobject_init, bfd_mach_o_get_base_address)
	(bfd_mach_o_lookup_command, bfd_mach_o_core_fetch_environment):
	Likewise.

binutils/
	* od-macho.c (dump_section_map): Adjust as load commands
	are now chained.
	(dump_load_command, dump_section_content): Likewise.