tree-ssa-operands.c (build_ssa_operands, [...]): Ignore a VIEW_CONVERT_EXPR on LHS when deciding if must or may def.

	PR/18664
	* tree-ssa-operands.c (build_ssa_operands, case MODIFY_EXPR):
	Ignore a VIEW_CONVERT_EXPR on LHS when deciding if must or may def.
	* tree-ssa-ccp.c (visit_assignment): If LHS is a VIEW_CONVERT_EXPR,
	add an inverse VIEW_CONVERT_EXPR to const_val.

From-SVN: r91450