Set wxUSE_CHOICEDLG to 1, I don't know why this is required I'll look at it later.

Originally committed to SVN as r3516.

aegisub/src/ffmpegsource_common.cpp

@@ -43,6 +43,9 @@
 #ifndef AGI_PRE
 #include <map>
 
+/// Force wx to use Choice Dialogue
+/// @todo Find out why this is needed.
+#define wxUSE_CHOICEDLG 1
 #include <wx/choicdlg.h>
 #include <wx/dir.h>
 #endif