Added a check for poll.h.

diff --git a/server/signal.c b/server/signal.c
index 0fe7df3..ea1c15b 100644
--- a/server/signal.c
+++ b/server/signal.c
@@ -22,6 +22,9 @@
 
 #include <signal.h>
 #include <stdio.h>
+#ifdef HAVE_POLL_H
+#include <poll.h>
+#endif
 #ifdef HAVE_SYS_POLL_H
 #include <sys/poll.h>
 #endif