BUG/MINOR: startup: fix allocation error message of progname string

Initially when init_early was introduced the progname string was a local
used for temporary storage of log_tag. Now it's global and detached from
log_tag enough. Thus, in the past we could inform that log_tag
allocation has been failed but not now.

Must be backported since the progname string became global, that is
v3.1-dev9-96-g49772c55e

src/haproxy.c

@@ -1436,7 +1436,7 @@ static void init_early(int argc, char **argv)
 	len = strlen(progname);
 	progname = strdup(progname);
 	if (!progname) {
-		ha_alert("Cannot allocate memory for log_tag.\n");
+		ha_alert("Cannot allocate memory for progname.\n");
 		exit(EXIT_FAILURE);
 	}