Include unistd.h for STDOUT_FILENO

STDOUT_FILENO is defined in unistd.h, see [POSIX](https://pubs.opengroup.org/onlinepubs/9799919799/).

This is required on FreeBSD.

src/compression_wrapper.c

@@ -26,6 +26,7 @@
 #include <stdio.h>
 #include <ctype.h>
 #include <stdbool.h>
+#include <unistd.h>
 #include <zlib.h>
 #include <bzlib.h>
 #include <lzma.h>