tree-data-ref.c (analyze_offset): Add a return value (bool) to indicate success/failure of the analysis.

	* tree-data-ref.c (analyze_offset): Add a return value (bool) to
	indicate success/failure of the analysis. Add negation to subtrahend
	in case of subtraction. Fail if both operands contain constants.
	(create_data_ref): Fail if analyze_offset fails.

From-SVN: r122817