* builtins.def (BUILT_IN_SIGNBIT, BUILT_IN_SIGNBITF,
	BUILT_IN_SIGNBITL): New GCC builtins.
	* builtins.c (expand_builtin_signbit): New function to RTL expand
	calls to signbit, signbitf and signbitl as inline intrinsics.
	(expand_builtin): Call expand_builtin_signbit for BUILT_IN_SIGNBIT*.
	(fold_builtin_signbit): New function to perform constant folding
	of signbit, signbitf and signbitl.
	(fold_builtin): Call fold_builtin_signbit for BUILT_IN_SIGNBIT*.

	* doc/extend.texi: Document new signbit{,f,l} builtins.

	* gcc.dg/builtins-1.c: Also test for __builtin_signbit{,f,l}.
	* gcc.dg/builtins-31.c: New testcase.
	* gcc.dg/builtins-32.c: New testcase.

From-SVN: r77070