lavu/file: include unistd.h only when available

The unistd.h header is only needed for the close() declaration.
If this header is not available, the close() declaration may be
provided by another header, e.g. io.h.

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavutil/file.c

@@ -20,7 +20,9 @@
 #include "log.h"
 #include <fcntl.h>
 #include <sys/stat.h>
+#if HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 #if HAVE_MMAP
 #include <sys/mman.h>
 #elif HAVE_MAPVIEWOFFILE