Make set_supplementary_gids return 'void'.

After https://android-review.googlesource.com/#/c/195351 lands,
no callers expect this function to return a result. Change the
signature to avoid errors.

Bug: 26099611
Change-Id: Id9c80350a0ce1f80ce5b5691117e68e37dd6c10e
diff --git a/libminijail.h b/libminijail.h
index ecc385a..fdd0d93 100644
--- a/libminijail.h
+++ b/libminijail.h
@@ -41,8 +41,8 @@
 void minijail_change_uid(struct minijail *j, uid_t uid);
 void minijail_change_gid(struct minijail *j, gid_t gid);
 /* Copies |list|. */
-int minijail_set_supplementary_gids(struct minijail *j, size_t size,
-				    const gid_t *list);
+void minijail_set_supplementary_gids(struct minijail *j, size_t size,
+				     const gid_t *list);
 /* Stores user to change to and copies |user| for internal consistency. */
 int minijail_change_user(struct minijail *j, const char *user);
 /* Does not take ownership of |group|. */