Turns out I wasn't building the syscall libraries. Do so.

plat/linux/libsys/isatty.c

@@ -0,0 +1,13 @@
+/* $Source: /cvsroot/tack/Ack/plat/linux386/libsys/isatty.c,v $
+ * $State: Exp $
+ * $Revision: 1.1 $
+ */
+
+#include <stdlib.h>
+#include <errno.h>
+#include <unistd.h>
+
+int isatty(int fd)
+{
+	return 0;
+}