BUILD: fix usage of ha_alert without format string

The compilation is failing due to no format string used in ha_alert.
This does not need to be backported.
diff --git a/src/cfgparse-global.c b/src/cfgparse-global.c
index 98012d1..b539a97 100644
--- a/src/cfgparse-global.c
+++ b/src/cfgparse-global.c
@@ -1310,7 +1310,7 @@
 					continue;
 				if (strcmp(kwl->kw[index].kw, args[0]) == 0) {
 					if (check_kw_experimental(&kwl->kw[index], file, linenum, &errmsg)) {
-						ha_alert(errmsg);
+						ha_alert("%s\n", errmsg);
 						err_code |= ERR_ALERT | ERR_FATAL;
 						goto out;
 					}
diff --git a/src/cfgparse-listen.c b/src/cfgparse-listen.c
index 78f1a58..525da58 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -3041,7 +3041,7 @@
 					continue;
 				if (strcmp(kwl->kw[index].kw, args[0]) == 0) {
 					if (check_kw_experimental(&kwl->kw[index], file, linenum, &errmsg)) {
-						ha_alert(errmsg);
+						ha_alert("%s\n", errmsg);
 						err_code |= ERR_ALERT | ERR_FATAL;
 						goto out;
 					}
diff --git a/src/haproxy.c b/src/haproxy.c
index 0ca8780..76fe08c 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -269,7 +269,7 @@
 {
 	if (kw->flags & KWF_EXPERIMENTAL) {
 		if (!experimental_directives_allowed) {
-			memprintf(errmsg, "parsing [%s:%d] : '%s' directive is experimental, must be allowed via a global 'expose-experimental-directives'\n",
+			memprintf(errmsg, "parsing [%s:%d] : '%s' directive is experimental, must be allowed via a global 'expose-experimental-directives'",
 			          file, linenum, kw->kw);
 			return 1;
 		}