Fix build on windows

DesktopEditor/agg-2.4/include/test_grads/custom_gradients.h

@@ -1,13 +1,22 @@
 #include <algorithm>
 #include <time.h>
+#include <math.h>
 #include "../../../graphics/AggPlusEnums.h"
 #ifndef M_1_PI
 #define M_1_PI 0.318309886183790671538
 #endif
 
 #ifndef NAN_FLOAT
+#ifdef NAN
+#define NAN_FLOAT NAN
+#else
 #define NAN_FLOAT 0.0f/0.0f
 #endif
+#endif
+
+#ifdef _WIN32
+#define isnanf _isnanf
+#endif
 
 #ifndef SHADING_PDF
 #define SHADING_PDF