[beast: 9/12] GXK: use std::isnan and std::isfinite

[Tim Janik <timj src gnome org>]

commit 923312ce5af039894da3a7f132ad174ce72909a3
Author: Tim Janik <timj gnu org>
Date:   Mon Sep 25 03:23:29 2017 +0200

    GXK: use std::isnan and std::isfinite
    
    Signed-off-by: Tim Janik <timj gnu org>

 beast-gtk/gxk/gxkspline.cc |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/beast-gtk/gxk/gxkspline.cc b/beast-gtk/gxk/gxkspline.cc
index 3316d12..a8975e6 100644
--- a/beast-gtk/gxk/gxkspline.cc
+++ b/beast-gtk/gxk/gxkspline.cc
@@ -1,9 +1,11 @@
 // Licensed GNU LGPL v2.1 or later: http://www.gnu.org/licenses/lgpl.html
-#define _ISOC99_SOURCE  /* NAN, isfinite, isnan */
 #include "gxkspline.hh"
 #include <stdlib.h>
 #include <string.h>
-#include <math.h>
+#include <cmath>
+
+using std::isnan;
+using std::isfinite;
 
 #define SQRT_3       (1.7320508075688772935274463415059)
 static const double INF = DBL_MAX;