[GHC] #15873: move to llvm 7 for 8.8.1

[GHC]

#15873: move to llvm 7 for 8.8.1
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        Reporter:  George            |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  high              |            Milestone:  8.8.1
       Component:  Compiler (LLVM)   |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by George):

 FWIW, llvm 7.0.1 seems to work with ghc 8.6.3 but I haven't done extensive
 testing.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15873#comment:2>
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