Typed hole inside typed Template Haskell bracket causes panic
When I say:
```hs
m :: a -> a
m x = $$([||_||])
```
I get:
```
T10946.hs:47:13:ghc: panic! (the 'impossible' happened)
(GHC version 7.10.1 for x86_64-unknown-linux):
No skolem info: a_apJ[sk]
```
This happens both with GHC 7.10.1 and latest HEAD (e2b579e8d77357e8b36f57d15daead101586ac8e).
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ---------------- |
| Version | 7.10.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | high |
| Resolution | Unresolved |
| Component | Template Haskell |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | goldfire |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"Typed hole inside typed Template Haskell bracket causes panic","status":"New","operating_system":"","component":"Template Haskell","related":[],"milestone":"8.0.1","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"7.10.1","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":["goldfire"],"type":"Bug","description":"When I say:\r\n\r\n{{{#!hs\r\nm :: a -> a\r\nm x = $$([||_||])\r\n}}}\r\nI get:\r\n{{{\r\nT10946.hs:47:13:ghc: panic! (the 'impossible' happened)\r\n (GHC version 7.10.1 for x86_64-unknown-linux):\r\n No skolem info: a_apJ[sk]\r\n}}}\r\nThis happens both with GHC 7.10.1 and latest HEAD (e2b579e8d77357e8b36f57d15daead101586ac8e).","type_of_failure":"OtherFailure","blocking":[]} -->
issue