PR 6811

	PR 6811
	* options.h (class Search_directory): Add is_system_directory.
	(class General_options): Declare is_in_system_directory.
	* options.cc (get_relative_sysroot): Make static.
	(get_default_sysroot): Make static.
	(General_optoins::is_in_system_directory): New function.
	* fileread.cc (Input_file::is_in_system_directory): New function.
	* fileread.h (class Input_file): Declare is_in_system_directory.
	* object.h (class Object): Add is_in_system_directory.
	(class Input_objects): Remove system_library_directory_ field.
	* object.cc (Input_objects::add_object): Don't set
	system_library_directory_.
	(input_objects::found_in_system_library_directory): Remove.
	* symtab.cc (Symbol_table::write_globals): Remove input_objects
	parameter.  Change all callers.
	(Symbol_table::sized_write_globals): Likewise.
	(Symbol_table::warn_about_undefined_dynobj_symbol): Likewise.
	Call Object::is_in_system_directory.
	* symtab.h (class Symbol_table): Update declarations.