swr-test: include opt.h, this is needed for changing options for testing.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswresample/swresample_test.c

@@ -21,6 +21,7 @@
 #include "libavutil/avassert.h"
 #include "libavutil/common.h"
 #include "libavutil/audioconvert.h"
+#include "libavutil/opt.h"
 #include "swresample.h"
 #undef fprintf