* c-common.c (warn_div_by_zero): New.
	* c-common.h (warn_div_by_zero): New.
	* c-decl.c (c_decode_option): Take it on the command line.
 	* c-typeck.c (build_binary_op): Warn about division by zero.
	* doc/invoke.texi: Document the new command line option, fix
	documentation of -Wmultichar.
 	* testsuite/gcc.dg/divbyzero.c: New tests.
 	* testsuite/gcc.dg/noncompile/20010524-1.c: Update.

From-SVN: r46439