* symtab.h (class Symbol_table): Add enum Defined.

	* symtab.h (class Symbol_table): Add enum Defined.
	* resolve.cc (Symbol_table::should_override): Add defined
	parameter.  Change all callers.  Test whether object is NULL
	before calling a method on it.
	(Symbol_table::report_resolve_problem): Add defined parameter.
	Change all callers.
	(Symbol_table::should_override_with_special): Likewise.
	* symtab.cc (Symbol_table::define_in_output_data): Add defined
	parameter.  Change all callers.
	(Symbol_table::do_define_in_output_data): Likewise.
	(Symbol_table::define_in_output_segment): Likewise.
	(Symbol_table::do_define_in_output_segment): Likewise.
	(Symbol_table::define_as_constant): Likewise.
	(Symbol_table::do_define_as_constant): Likewise.
	* script.h (class Symbol_assignment): Add is_defsym parameter to
	constructor; change all callers.
	* script.cc (Script_options::add_symbol_assignment): Add is_defsym
	parameter.  Change all callers.  Add is_defsym_ field.
	(class Parser_closure): Add parsing_defsym parameter to
	constructor; change all callers.  Add parsing_defsym accessor
	function.  Add parsing_defsym_ field.