cvdef.h: Don't use C's limits.h under C++

Just like with the other headers in the rest of the file.

See e.g. https://stackoverflow.com/questions/36831465/what-difference-does-it-make-when-i-include-limits-or-limits-h-in-my-c-cod
for the reasons, the most important one being that limits.h does not respect
namespaces, which can make problems for downstream consumers of cvdef.h.

modules/core/include/opencv2/core/cvdef.h

@@ -181,7 +181,12 @@ namespace cv {
 #undef abs
 #undef Complex
 
+#if defined __cplusplus
+#include <limits>
+#else
 #include <limits.h>
+#endif
+
 #include "opencv2/core/hal/interface.h"
 
 #if defined __ICL