thread blocked when running `deepseq` with infinite list
```hs
ghci> :m +Control.Deepseq
ghci> let x = [1..]
ghci> x `deepseq` ()
Ctrl^C
Interrupted.
ghci>
ghc.exe: panic! (the 'impossible' happened)
(GHC version 8.0.2 for x86_64-unknown-mingw32):
thread blocked indefinitely in an MVar operation
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
```
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ---------------- |
| Version | 8.0.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | Unknown/Multiple |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"thread blocked when running `deepseq` with infinite list","status":"New","operating_system":"Unknown/Multiple","component":"Compiler","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.0.2","keywords":["blocked","thread"],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"{{{#!hs\r\nghci> :m +Control.Deepseq\r\nghci> let x = [1..]\r\nghci> x `deepseq` ()\r\nCtrl^C\r\nInterrupted.\r\nghci>\r\nghc.exe: panic! (the 'impossible' happened)\r\n (GHC version 8.0.2 for x86_64-unknown-mingw32):\r\n thread blocked indefinitely in an MVar operation\r\n\r\nPlease report this as a GHC bug: http://www.haskell.org/ghc/reportabug\r\n}}}","type_of_failure":"OtherFailure","blocking":[]} -->
issue