Fix C99 declaration.

Bug: 26040155
Change-Id: I5779d447d0c4917b30093a435db680fe3f66c8b3
diff --git a/libminijail.c b/libminijail.c
index e988c00..6de6b6a 100644
--- a/libminijail.c
+++ b/libminijail.c
@@ -197,6 +197,8 @@
 int API minijail_set_supplementary_gids(struct minijail *j, size_t size,
 					const gid_t *list)
 {
+	size_t i;
+
 	if (j->flags.usergroups)
 		die("cannot inherit *and* set supplementary groups");
 
@@ -208,7 +210,7 @@
 	if (!j->suppl_gid_list) {
 		return -ENOMEM;
 	}
-	for (size_t i = 0; i < size; i++) {
+	for (i = 0; i < size; i++) {
 		j->suppl_gid_list[i] = list[i];
 	}
 	j->suppl_gid_count = size;