avdevice/dshow: fix build, ensure that feature enable #defines are set before includes

dshow_capture.h sets up various flags before including windows headers
this must occur before other headers (like os_support.h) include these
headers without the setup

This could be fixed differently but for now this fixes building on mingw
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/dshow.c

@@ -19,13 +19,13 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "dshow_capture.h"
 #include "libavutil/parseutils.h"
 #include "libavutil/pixdesc.h"
 #include "libavutil/opt.h"
 #include "libavformat/internal.h"
 #include "libavformat/riff.h"
 #include "avdevice.h"
-#include "dshow_capture.h"
 #include "libavcodec/raw.h"
 
 struct dshow_ctx {