doc/print_options: Fix build on mingw after 960aff37

A cleaner fix is very welcome
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/print_options.c

@@ -26,6 +26,10 @@
 #include <string.h>
 #include <float.h>
 
+// print_options is build for the host, os_support.h isnt needed and is setup
+// for the target. without this build breaks on mingw
+#define AVFORMAT_OS_SUPPORT_H
+
 #include "libavformat/avformat.h"
 #include "libavformat/options_table.h"
 #include "libavcodec/avcodec.h"