tree-ssa-math-opts.c (convert_plusminus_to_widen): Fix type used in the call to optab_for_tree_code.

gcc/
	* tree-ssa-math-opts.c (convert_plusminus_to_widen): Fix type
	used in the call to optab_for_tree_code.  Fix the second
	is_widening_mult_p call.  Check that both unwidened operands
	have the same sign.

From-SVN: r162784