Make literal_unroll function work as a freevar.

As title. For context see comment on numba#5626.

numba/core/untyped_passes.py

@@ -615,7 +615,7 @@ def run_pass(self, state):
             calls = [_ for _ in blk.find_exprs('call')]
             for call in calls:
                 glbl = guard(get_definition, func_ir, call.func)
-                if glbl and isinstance(glbl, ir.Global):
+                if glbl and isinstance(glbl, (ir.Global, ir.FreeVar)):
                     # find a literal_unroll
                     if glbl.value is literal_unroll:
                         if len(call.args) > 1:
@@ -1285,7 +1285,8 @@ def assess_loop(self, loop, func_ir, partial_typemap=None):
                         return False
                     func_var = guard(get_definition, func_ir,  call.func)
                     func = guard(get_definition, func_ir,  func_var)
-                    if func is None or not isinstance(func, ir.Global):
+                    if func is None or not isinstance(func,
+                                                      (ir.Global, ir.FreeVar)):
                         return False
                     if (func.value is None or
                             func.value not in self._accepted_calls):

numba/tests/test_mixed_tuple_unroller.py

@@ -1801,6 +1801,19 @@ def foo(cont):
             ['a', '25', '0.23', 'None'],
         )
 
+    def test_unroll_freevar_tuple(self):
+        mixed = (np.ones((1,)), np.ones((1, 1)), np.ones((1, 1, 1)))
+        from numba import literal_unroll as freevar_unroll
+
+        @njit
+        def foo():
+            out = 0
+            for i in freevar_unroll(mixed):
+                out += i.ndim
+            return out
+
+        self.assertEqual(foo(), foo.py_func())
+
 
 def capture(real_pass):
     """ Returns a compiler pass that captures the mutation state reported