file: Add S_ISFIFO compatability macro

Not all systems have S_ISFIFO.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/file.c

@@ -33,6 +33,14 @@
 #include "os_support.h"
 #include "url.h"
 
+/* Some systems may not have S_ISFIFO */
+#ifndef S_ISFIFO
+#  ifdef S_IFIFO
+#    define S_ISFIFO(m) (((m) & S_IFMT) == S_IFIFO)
+#  else
+#    define S_ISFIFO(m) 0
+#  endif
+#endif
 
 /* standard file protocol */