unix: djgpp errno.h have no ENOTSUP, so define it to Linux value.

unix/mpconfigport_freedos.h

@@ -36,3 +36,9 @@
 
 // djgpp dirent struct does not have d_ino field
 #undef _DIRENT_HAVE_D_INO
+
+// djgpp errno.h have no ENOTSUP
+#include <errno.h>
+#ifndef ENOTSUP
+#define ENOTSUP 88
+#endif