Fix compile error on opensuse 12.2 with systemd 44 and glibc-2.15.

The specific systemd/glibc version do not include syslog.h by default.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=73455Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

dbus/dbus-spawn.c

@@ -39,6 +39,9 @@
 #include <errno.h>
 #endif
 #ifdef HAVE_SYSTEMD
+#ifdef HAVE_SYSLOG_H
+#include <syslog.h>
+#endif
 #include <systemd/sd-journal.h>
 #endif