made FLANN (and dependent on it code) build fine on Windows. Most of the changes are added CV_EXPORTS' into the class declarations and extern variables are turned into external functions (as a nice side effect the variables are now read-only)

modules/flann/include/opencv2/flann/timer.h

@@ -42,7 +42,7 @@ namespace cvflann
  *
  * Can be used to time portions of code.
  */
-class StartStopTimer
+class CV_EXPORTS StartStopTimer
 {
     clock_t startTime;