Syslogger chooses incorrect name for alert file

Error was introduced by PG 8.3 merge. In Postgres there is only one
log, and its name pattern is set by global variable Log_filename.
But in GPDB there is a separate alert log used by gpperfmon, and its
file name is also generated by logfile_getname() function, and you
have to use the passed pattern instead of global variable as a file
name pattern, as alert filename pattern is "gpdb-alert-..."

src/backend/postmaster/syslogger.c

@@ -2106,7 +2106,7 @@ logfile_getname(pg_time_t timestamp, const char *suffix, const char *log_directo
     if (strchr(log_file_pattern, '%'))
     {
         /* treat it as a strftime pattern */
-		pg_strftime(filename + len, MAXPGPATH - len, Log_filename,
+		pg_strftime(filename + len, MAXPGPATH - len, log_file_pattern,
 				   pg_localtime(&timestamp, log_timezone));
     }
     else