msdk: Fix building on MSVC

And add missing #ifdef _WIN32 for MSVC build

https://bugzilla.gnome.org/show_bug.cgi?id=797211

sys/msdk/gstmsdkenc.c

@@ -1096,6 +1096,7 @@ gst_msdkenc_get_surface_from_pool (GstMsdkEnc * thiz, GstBufferPool * pool,
   return msdk_surface;
 }
 
+#ifndef _WIN32
 static gboolean
 import_dmabuf_to_msdk_surface (GstMsdkEnc * thiz, GstBuffer * buf,
     MsdkSurface * msdk_surface)
@@ -1156,6 +1157,7 @@ import_dmabuf_to_msdk_surface (GstMsdkEnc * thiz, GstBuffer * buf,
 
   return TRUE;
 }
+#endif
 
 static MsdkSurface *
 gst_msdkenc_get_surface_from_frame (GstMsdkEnc * thiz,

sys/msdk/gstmsdksystemmemory.c

@@ -30,7 +30,9 @@
  * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#ifndef _WIN32
 #include <unistd.h>
+#endif
 #include <stdlib.h>
 #include "gstmsdksystemmemory.h"
 

sys/msdk/gstmsdkvideomemory.c

@@ -30,9 +30,11 @@
  * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#ifndef _WIN32
 #include <unistd.h>
-#include <stdlib.h>
 #include <va/va.h>
+#endif
+#include <stdlib.h>
 #include "gstmsdkvideomemory.h"
 #include "gstmsdkallocator.h"
 

sys/msdk/gstmsdkvpp.c

@@ -513,6 +513,7 @@ get_surface_from_pool (GstMsdkVPP * thiz, GstBufferPool * pool,
   return msdk_surface;
 }
 
+#ifndef _WIN32
 static gboolean
 import_dmabuf_to_msdk_surface (GstMsdkVPP * thiz, GstBuffer * buf,
     MsdkSurface * msdk_surface)
@@ -576,6 +577,7 @@ import_dmabuf_to_msdk_surface (GstMsdkVPP * thiz, GstBuffer * buf,
 
   return TRUE;
 }
+#endif
 
 static MsdkSurface *
 get_msdk_surface_from_input_buffer (GstMsdkVPP * thiz, GstBuffer * inbuf)