watchdog: Enable --with-watchdog[=DEV] and improve log messages

This patch changes the configure option to enable the built-in watchdog
from --enable-watchdog to --with-watchdog[=DEV].  This is the convention
for features that take arguments.

Also, improve log messages to aid debugging when finit-watchdogd does
not start properly.  This means flushing logs to syslogd with closelog()

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/watchdog.h

@@ -23,7 +23,9 @@
 
 #include "config.h"		/* Generated by configure script */
 
+#ifndef WDT_DEVNODE
 #define WDT_DEVNODE "/dev/watchdog"
+#endif
 #define WDT_TIMEOUT 30
 
 /**