Add files from 'copysign' and 'isfinite' Gnulib modules.

* lib/copysign.c:
* lib/isfinite.c:
* lib/isnanf-nolibm.h:
* lib/isnanl-nolibm.h:
* lib/signbitd.c:
* lib/signbitf.c:
* lib/signbitl.c:
* m4/copysign.m4:
* m4/isfinite.m4:
* m4/signbit.m4: New files.

lib/copysign.c

@@ -0,0 +1,26 @@
+/* Copy sign into another 'double' number.
+   Copyright (C) 2011-2013 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <math.h>
+
+double
+copysign (double x, double y)
+{
+  return (signbit (x) != signbit (y) ? - x : x);
+}