Handle isnan at a more central place.

Do not distribute architecture specific
code across a lot of places.

simgear/math/SGGeod.hxx

@@ -20,10 +20,6 @@
 
 #include <simgear/constants.h>
 
-#ifndef _MSC_VER
-using std::isnan;
-#endif
-
 // #define SG_GEOD_NATIVE_DEGREE
 
 /// Class representing a geodetic location
@@ -356,7 +352,10 @@ inline
 bool
 SGGeod::isValid() const
 {
-  if (isnan(_lon) || isnan(_lat)) return false;
+  if (SGMiscd::isNaN(_lon))
+      return false;
+  if (SGMiscd::isNaN(_lat))
+      return false;
 #ifdef SG_GEOD_NATIVE_DEGREE
   return (_lon >= -180.0) && (_lon <= 180.0) &&
   (_lat >= -90.0) && (_lat <= 90.0);

simgear/math/SGMisc.hxx

@@ -92,7 +92,6 @@ public:
   static S lerp(const S& val0, const S& val1, const T& t)
   { return val0*(T(1) - t) + val1*t; }
 
-#ifndef NDEBUG
   /// Returns true if v is a NaN value
   /// Use with care: allways code that you do not need to use that!
   static bool isNaN(const T& v)
@@ -109,7 +108,6 @@ public:
     return !(v == v);
 #endif
   }
-#endif
 };
 
 #endif