Submitted for upstream inclusion at:
https://github.com/eclipse/mosquitto/pull/361

diff -u -r ../mosquitto-1.4.10/src/conf.c ./src/conf.c
--- ../mosquitto-1.4.10/src/conf.c	2016-08-17 13:05:14.000000000 +0200
+++ ./src/conf.c	2017-01-24 10:50:34.011878190 +0100
@@ -36,7 +36,7 @@
 #endif
 
 #if !defined(WIN32) && !defined(__CYGWIN__)
-#  include <sys/syslog.h>
+#  include <syslog.h>
 #endif
 
 #include <mosquitto_broker.h>