ismindex: Replace mkdir ifdeffery by os_support.h #include

os_support.h contains more precise workarounds for non-POSIX mkdir().

tools/ismindex.c

@@ -34,13 +34,9 @@
 
 #include <stdio.h>
 #include <string.h>
-#include <sys/stat.h>
-#ifdef _WIN32
-#include <direct.h>
-#define mkdir(a, b) _mkdir(a)
-#endif
 
 #include "libavformat/avformat.h"
+#include "libavformat/os_support.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/mathematics.h"