dshow_filter: fix compilation with mingw-w64

Closes ticket #999
NO_DSHOW_STRSAFE asks dshow.h header to not use secure string function
replacements.
Using secure replacements would break mingw.org compatibility as they don't
declare/define those functions.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/dshow_filter.c

@@ -19,6 +19,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#define NO_DSHOW_STRSAFE
 #include "dshow.h"
 
 DECLARE_QUERYINTERFACE(libAVFilter,

libavdevice/dshow_pin.c

@@ -19,6 +19,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#define NO_DSHOW_STRSAFE
 #include "dshow.h"
 
 #include <stddef.h>