define correct isnan, isinf functions

src/CanvasRenderingContext2d.cc

@@ -23,11 +23,16 @@
 #endif
 
 // Windows doesn't support the C99 names for these
-#ifndef isnan
+#ifdef _MSC_VER
 #define isnan(x) _isnan(x)
 #define isinf(x) (!_finite(x))
 #endif
 
+#ifndef isnan
+#define isnan(x) std::isnan(x)
+#define isinf(x) std::isinf(x)
+#endif
+
 Persistent<FunctionTemplate> Context2d::constructor;
 
 /*