re PR middle-end/81914 (gcc 7.1 generates branch for code which was branchless in earlier gcc version)

	PR middle-end/81914
	* predict.c (zero_one_minusone): New function.
	(apply_return_prediction): Avoid return prediction for functions
	returning only -1, 0 and 1 values, unless they only return -1 and 0
	or 0 and 1.

From-SVN: r255829