syslog.h: missing LOG_MAKEPRI definition

Bug: 19681572
Change-Id: Ice5f5cb1f71522ffc47b2243a8dc4c277c2a288f
diff --git a/libc/include/syslog.h b/libc/include/syslog.h
index cbceab2..8000f03 100644
--- a/libc/include/syslog.h
+++ b/libc/include/syslog.h
@@ -47,6 +47,7 @@
 
 #define LOG_PRIMASK 7
 #define LOG_PRI(x) ((x) & LOG_PRIMASK)
+#define LOG_MAKEPRI(fac, pri) ((fac) | (pri))
 
 /* Facilities are currently ignored on Android. */
 #define LOG_KERN     0000