Add configure test for the 'sigaction' function.
diff --git a/config_in.h b/config_in.h
index 5951861..be3459b 100644
--- a/config_in.h
+++ b/config_in.h
@@ -54,6 +54,9 @@
 /* Define to 1 if you have the <netinet/in.h> header file. */
 #undef HAVE_NETINET_IN_H
 
+/* Define to 1 if you have the `sigaction' function. */
+#undef HAVE_SIGACTION
+
 /* Define to 1 if you have the `socket' function. */
 #undef HAVE_SOCKET