Fix compilation issue with MinGW (disables the usage of strsafe.h).

Recent versions of MinGW include strsafe.h in dshow.h.
strsafe.h undefines all non-safe string functions, including
vsprintf and others, to prevent their usage. This causes
QString and others to fail. Defining NO_DSHOW_STRSAFE before
including dshow.h prevents this behaviour.

Change-Id: I012fecbabc5c11900486c1dfdc970a00613ef6f7
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/plugins/directshow/directshow.pro

@@ -17,6 +17,10 @@ SOURCES += dsserviceplugin.cpp
     DEFINES += HAVE_WIDGETS
 }
 
+win32-g++ {
+    DEFINES += NO_DSHOW_STRSAFE
+}
+
 !config_wmf: include(player/player.pri)
 include(camera/camera.pri)