Add a broken test for lingering state from TH unique names #9693

The stderr output is

```
Loading with T9693_initial.hs

T9693_main.hs:4:1:
    Same exact name in multiple name-spaces:
      type constructor or class ‘X’, declared at: T9693_main.hs:4:1
      data constructor ‘X’, declared at: T9693_main.hs:4:1
      Probable cause: you bound a unique Template Haskell name (NameU),
      perhaps via newName, in different name-spaces.
      If that's it, then -ddump-splices might be useful
Reloading with T9693_modified.hs

T9693_main.hs:1:1:
    Data constructor ‘X’ used as a type constructor
```

The strange thing is that the modified version uses (mkName "X"), which should
be fine for simultaneous use in both a data constructor and type constructor.
Indeed, on a fresh load, the modified version works fine. So there is some sort
of state left over from the prior load when (newName "X") was used.

Test Plan: testsuite/tests/th/T9693.script

Reviewers: bgamari, sighingnow, RyanGlScott

Reviewed By: sighingnow, RyanGlScott

Subscribers: RyanGlScott, sighingnow, rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4926

1 files changed, 4 insertions, 0 deletions

diff --git a/testsuite/tests/th/T9693_main.hs b/testsuite/tests/th/T9693_main.hs
new file mode 100644
index 0000000000..71e7c9a3c7
--- /dev/null
+++ b/testsuite/tests/th/T9693_main.hs
@@ -0,0 +1,4 @@
+{-# LANGUAGE TemplateHaskell #-}
+import T9693
+
+stuff