Update file_dialog_save.cpp

added defined on line 37

Former-commit-id: be655601d21f29b949e8bfb8e7f08747fe2f0c25

include/igl/file_dialog_save.cpp

@@ -34,7 +34,7 @@ IGL_INLINE std::string igl::file_dialog_save()
   while ( fgets(buffer, FILE_DIALOG_MAX_BUFFER, output) != NULL )
   {
   }
-#elif _WIN32
+#elif defined _WIN32
 
   // Use native windows file dialog box
   // (code contributed by Tino Weinkauf)