* fold-const.c (fold_comparison): Fold ~X op ~Y as Y op X.
	Fold ~X op C as X op' ~C, where op' is the swapped comparison.
	(fold_binary): ~X eq/ne C is now handled in fold_comparison.
	Fold -X eq/ne -Y as X eq/ne Y.

	* gcc.dg/fold-compare-1.c: New test case.

From-SVN: r118158