T4120 passes now! Hooray

testsuite/tests/indexed-types/should_compile/T4120.stderr

-
-T4120.hs:17:10:
-    Couldn't match expected type `forall s. MVector s a'
-                with actual type `forall s. Mutable Vector s a0'
-    Expected type: (forall s. MVector s a) -> Int
-      Actual type: (forall s. Mutable Vector s a0) -> Int
-    In the expression: create1
-    In an equation for `create': create = create1

testsuite/tests/indexed-types/should_compile/all.T

@@ -146,7 +146,7 @@ test('IndTypesPerf',
      run_command,
      ['$MAKE -s --no-print-directory IndTypesPerf'])
 
-test('T4120', normal, compile_fail, [''])
+test('T4120', normal, compile, [''])
 test('T3787', reqlib('mtl'), compile, [''])
 test('T3826', normal, compile, [''])
 test('T4200', normal, compile, [''])