skip rvm example build with simpleocv

examples/CMakeLists.txt

@@ -46,9 +46,6 @@ if(NCNN_PIXEL)
         ncnn_add_example(rfcn)
         ncnn_add_example(yolov2)
         ncnn_add_example(yolov3)
-        if(OpenCV_FOUND)
-            ncnn_add_example(yolov4)
-        endif()
         ncnn_add_example(yolov5)
         ncnn_add_example(yolox)
         ncnn_add_example(mobilenetv2ssdlite)
@@ -62,7 +59,10 @@ if(NCNN_PIXEL)
         ncnn_add_example(nanodet)
         ncnn_add_example(scrfd)
         ncnn_add_example(scrfd_crowdhuman)
-        ncnn_add_example(rvm)
+        if(OpenCV_FOUND)
+            ncnn_add_example(yolov4)
+            ncnn_add_example(rvm)
+        endif()
     else()
         message(WARNING "OpenCV not found and NCNN_SIMPLEOCV disabled, examples won't be built")
     endif()