* real.c (real_floor, real_ceil): Tweak to allow input and output
	arguments to overlap.
	(real_round): New function to implement round(3m) semantics.
	* real.h (real_round): Prototype here.
	* builtins.c (fold_builtin_round): New function to constant fold
	round, roundf and roundl.
	(fold_builtin): Call fold_builtin_round for BUILT_IN_ROUND{,F,L}.

	* gcc.dg/builtins-29.c: New test case.

From-SVN: r76428