[GHC] #9050: Panic when compiling cmm file together with -outputdir

[GHC]

#9050: Panic when compiling cmm file together with -outputdir
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       Reporter:  Yuras            |             Owner:
           Type:  bug              |            Status:  new
       Priority:  normal           |         Milestone:
      Component:  Compiler         |           Version:  7.8.2
       Keywords:                   |  Operating System:  Unknown/Multiple
   Architecture:                   |   Type of failure:  Compile-time crash
  Unknown/Multiple                 |         Test Case:
     Difficulty:  Unknown          |          Blocking:
     Blocked By:                   |
Related Tickets:                   |
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 To reproduce:

 {{{
 $ touch test.cmm
 $ ghc -c test.cmm -outputdir=build
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 7.9.20140428 for x86_64-unknown-linux):
         hscCmmFile: no_mod
 }}}

 The panic is declared in `main/HscMain.hs:hscCompileCmmFile` in place of
 current module name, but forced in
 `main/CodeOutput.lhs:outputForeignStubs` by `doesFileExist`.

 It works without `-outputdir` because in that case module name is not used
 to create path to stub file, see `main/Finder.lhs:mkStubPaths`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9050>
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