configure: Store vda lib flags in extralibs instead of ldflags

This way the needed linking flags end up in libavcodec.pc.
Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -3002,7 +3002,7 @@ check_func XFixesGetCursorImage -lX11 -lXext -lXfixes
 
 # check for VDA header
 if ! disabled vda && check_header VideoDecodeAcceleration/VDADecoder.h; then
-    enable vda && add_ldflags -framework CoreFoundation -framework VideoDecodeAcceleration -framework QuartzCore
+    enable vda && add_extralibs -framework CoreFoundation -framework VideoDecodeAcceleration -framework QuartzCore
 fi
 
 if ! disabled vdpau && enabled vdpau_vdpau_h; then