[GHC] #5169: LLVM backend should warn if llvm tools aren't installed

[GHC]

#5169: LLVM backend should warn if llvm tools aren't installed
---------------------------------+------------------------------------------
    Reporter:  dterei            |       Owner:              
        Type:  feature request   |      Status:  new         
    Priority:  normal            |   Component:  Compiler    
     Version:  7.0.3             |    Keywords:              
    Testcase:                    |   Blockedby:              
          Os:  Unknown/Multiple  |    Blocking:              
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
---------------------------------+------------------------------------------
 At the moment the LLVM backend just assumes that the various LLVM tools
 will be available on the command line. It never checks for this and so if
 you try to compile some code using the LLVM backend without LLVM tools
 available on the command line then it fails with:

 {{{
 cannot run: opt
 }}}

 We should print something more informative.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5169>
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