PR 10860

	PR 10860
	* options.h (class General_options): Add --warn-common.
	* resolve.cc (Symbol_table::resolve): Handle --warn-common when
	merging two common symbols.
	(Symbol_table::should_override): Handle --warn-common when merging
	a common symbol with a defined symbol.  Use report_resolve_problem
	for multiple definitions.
	(Symbol_table::report_resolve_problem): New function.
	* symtab.h (class Symbol_table): Declare report_resolve_problem.