logd: add internal prdebug function

Usage: android::prdebug(const char *fmt, ...) __printflike(1, 2);

Will add logd prefix tag, log as debug priority in kernel logs,
and will suffix a newline if one is not supplied. To be used to
aid debugging of the logger only.

Change-Id: I217326ef34dc4eb0ea076bacb7a7a8b564c931c3
diff --git a/logd/LogUtils.h b/logd/LogUtils.h
index fd4800e..aa4b6e1 100644
--- a/logd/LogUtils.h
+++ b/logd/LogUtils.h
@@ -17,6 +17,7 @@
 #ifndef _LOGD_LOG_UTILS_H__
 #define _LOGD_LOG_UTILS_H__
 
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
 #include <log/log.h>
@@ -29,6 +30,7 @@
 
 // Furnished in main.cpp. Caller must own and free returned value
 char *uidToName(uid_t uid);
+void prdebug(const char *fmt, ...) __printflike(1, 2);
 
 // Furnished in LogStatistics.cpp. Caller must own and free returned value
 char *pidToName(pid_t pid);