Add testcase for #5948.

testsuite/tests/polykinds/T5948.hs

+{-# LANGUAGE DataKinds, TypeOperators #-}
+
+module T5948 where
+
+type Foo = (Int ': '[])
+
+type Bar = Int ': '[]

testsuite/tests/polykinds/all.T

@@ -31,5 +31,4 @@ test('T5881', normal, run_command, ['$MAKE -s --no-print-directory T5881'])
 test('T5716', normal, compile_fail, [''])
 test('T5937', normal, compile, [''])
 test('T5935', normal, compile, [''])
-
-
+test('T5948', normal, compile, [''])