Add fallback implemetation for rint()/round()

Add an implementation for rint() and round() for compilers that do not
define one or both of them.  Note that this file should be included
after config.h was included.

gtk/fallback-c89.c

@@ -0,0 +1,58 @@
+/* GTK - The GIMP Toolkit
+ * Copyright (C) 2011 Chun-wei Fan <fanc999@yahoo.com.tw>
+ *
+ * Author: Chun-wei Fan <fanc999@yahoo.com.tw>
+ *
+ * This library 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 2 of the License, or (at your option) any later version.
+ *
+ * This library 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 library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include <math.h>
+ 
+/* Workaround for round() for non-GCC/non-C99 compilers */
+#ifndef HAVE_ROUND
+static inline double
+round (double x)
+{
+  if (x >= 0)
+    return floor (x + 0.5);
+  else
+    return ceil (x - 0.5);
+}
+#endif
+
+/* Workaround for rint() for non-GCC/non-C99 compilers */
+#ifndef HAVE_RINT
+static inline double
+rint (double x)
+{
+  if (ceil (x + 0.5) == floor (x + 0.5))
+  {
+    int a;
+    a = (int) ceil (x);
+    if (a % 2 == 0)
+      return ceil (x);
+    else
+      return floor (x);
+  }
+  else
+  {
+    if (x >= 0)
+      return floor (x + 0.5);
+    else
+      return ceil (x - 0.5);
+  }
+}
+#endif