ghci always recompiles source files even if there are .o files
In 8.2.1-rc1 loading a file compiled with -O2 into ghci results in ghci recompiling the file into interpreted byte code. In 8.0.2 it simply loads the compiled object file.
1. 2.1
```
ghc -dynamic -O2 eh2.hs
[1 of 1] Compiling Main ( eh2.hs, eh2.o )
Linking eh2 ...
bash-3.2$ ghci -ignore-dot-ghci
GHCi, version 8.2.0.20170404: http://www.haskell.org/ghc/ :? for help
Prelude> :load eh2
[1 of 1] Compiling Main ( eh2.hs, interpreted ) [flags changed]
Ok, modules loaded: Main.
```
1. 0.2
```
ghc --version
The Glorious Glasgow Haskell Compilation System, version 8.0.2
bash-3.2$ pwd
/Users/gcolpitts/haskell
bash-3.2$ ghc -dynamic -O2 eh2.hs
[1 of 1] Compiling Main ( eh2.hs, eh2.o )
Linking eh2 ...
bash-3.2$ ghci -ignore-dot-ghci
GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help
Prelude> :load eh2
Ok, modules loaded: Main (eh2.o).
```
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ------------ |
| Version | 8.0.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | GHCi |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"regression in ghc 8.2.1-rc1 (8.2.0.2017040)","status":"New","operating_system":"","component":"GHCi","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.0.1","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"In 8.2.1-rc1 loading a file compiled with -O2 into ghci results in ghci recompiling the file into interpreted byte code. In 8.0.2 it simply loads the compiled object file.\r\n\r\n8.2.1\r\n{{{\r\n ghc -dynamic -O2 eh2.hs\r\n[1 of 1] Compiling Main ( eh2.hs, eh2.o )\r\nLinking eh2 ...\r\nbash-3.2$ ghci -ignore-dot-ghci\r\nGHCi, version 8.2.0.20170404: http://www.haskell.org/ghc/ :? for help\r\nPrelude> :load eh2\r\n[1 of 1] Compiling Main ( eh2.hs, interpreted ) [flags changed]\r\nOk, modules loaded: Main.\r\n}}}\r\n\r\n8.0.2 \r\n\r\n{{{\r\n ghc --version\r\nThe Glorious Glasgow Haskell Compilation System, version 8.0.2\r\nbash-3.2$ pwd\r\n/Users/gcolpitts/haskell\r\nbash-3.2$ ghc -dynamic -O2 eh2.hs\r\n[1 of 1] Compiling Main ( eh2.hs, eh2.o )\r\nLinking eh2 ...\r\nbash-3.2$ ghci -ignore-dot-ghci\r\nGHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help\r\nPrelude> :load eh2\r\nOk, modules loaded: Main (eh2.o).\r\n}}}","type_of_failure":"OtherFailure","blocking":[]} -->
issue