Fix MSVC compilation, thanks to Fred.

diff --git a/simgear/sound/sample_group.cxx b/simgear/sound/sample_group.cxx
index c91ca5430f79f8aeda5c7cfd0ff1d5f08431f90c..78efd1675efa71718e6956ba21d5208f1e24aae1 100644 (file)
--- a/simgear/sound/sample_group.cxx
+++ b/simgear/sound/sample_group.cxx
@@ -34,7 +34,10 @@
 #include "sample_group.hxx"
 
 using std::string;
+
+#ifdef HAVE_STD_ISNAN
 using std::isnan;
+#endif
 
 bool isNaN(float *v) {
    return (isnan(v[0]) || isnan(v[1]) || isnan(v[2]));