Fix %concatenate-to-vector

src/code/seq.lisp

@@ -1169,8 +1169,9 @@ many elements are copied."
     (declare (index length))
     (do-rest-arg ((seq) sequences)
       (incf length (length seq)))
-    (let ((result (sb-vm::allocate-vector-with-widetag #+ubsan nil
-                                                       widetag length nil))
+    (let* ((n-bits-shift (aref sb-vm::%%simple-array-n-bits-shifts%% widetag))
+           (result (sb-vm::allocate-vector-with-widetag
+                    #+ubsan nil widetag length n-bits-shift))
            (setter (the function (svref %%data-vector-setters%% widetag)))
            (index 0))
       (declare (index index))

tests/vector.pure.lisp

@@ -69,3 +69,7 @@
                                 (setf (fill-pointer x) 0)))
             (make-array 2 :adjustable t))
    type-error))
+
+(with-test (:name :concatenate-to-vector)
+  (assert (sb-kernel:%concatenate-to-vector sb-vm:simple-bit-vector-widetag
+                                           '(1 1) '(1 0))))