main: add option to print configuration

Add -p option to chronyd to print lines from the configuration as they
are parsed and exit. It can be used to verify the syntax and get the
whole configuration when it is split into multiple files.

conf.h

@@ -35,6 +35,8 @@
 extern void CNF_Initialise(int restarted, int client_only);
 extern void CNF_Finalise(void);
 
+extern void CNF_EnablePrint(void);
+
 extern char *CNF_GetRtcDevice(void);
 
 extern void CNF_ReadFile(const char *filename);