* common.opt (Woverflow): New command line option.
	* c-common.c (constant_expression_warning): Check warn_overflow.
	(overflow_waring): Pass OPT_Woverflow to warning.
	(unsigned_conversion_warning): Likewise.
	(convert_and_check): Likewise.
	* doc/invoke.texi: Document new command line option.

	* gcc.dg/Woverflow-1.c: New test case.
	* gcc.dg/Woverflow-2.c: Likewise.
	* gcc.dg/Woverflow-3.c: Likewise.

From-SVN: r113408