fixed gcc dwarf2 check

CMakeLists.txt

@@ -366,7 +366,13 @@ set(WITH_EIGEN ON CACHE BOOL "Include Eigen2/Eigen3 support")
 set(WITH_CUDA ON CACHE BOOL "Include NVidia Cuda Runtime support")
 
 if(WIN32)
-    if (MINGW AND ${CMAKE_OPENCV_GCC_INFO_FULL} MATCHES "--with-dwarf2")
+    set(MINGW_DWARF2 0)
+    if (MINGW)
+        if(${CMAKE_OPENCV_GCC_INFO_FULL} MATCHES "--with-dwarf2")
+            set(MINGW_DWARF2 1)
+        endif()
+    endif()
+    if (MINGW_DWARF2)
 		set(WITH_VIDEOINPUT OFF CACHE BOOL "Enable VideoInput support")
 	else()
 		set(WITH_VIDEOINPUT ON CACHE BOOL "Enable VideoInput support")