re PR tree-optimization/14846 ([tree-ssa] don't use a shift in A & CST_POWER_OF_2 == 0 until very late in tree-ssa optimizations)

	PR tree-optimization/14846
	* fold-const.c (fold_single_bit_test_into_sign_test): New,
	split out from ...
	(fold_single_bit_test): ... here.
	(fold_binary): Call fold_single_bit_test_into_sign_test
	instead of fold_single_bit_test.

From-SVN: r98482