[MacPorts] #52551: ghc: bump llvm dep

[MacPorts]

#52551: ghc: bump llvm dep
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  Reporter:  grimreaper  |      Owner:  neverpanic
      Type:  defect      |     Status:  reopened
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.3.4
Resolution:              |   Keywords:  haspatch
      Port:  ghc         |
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Comment (by jeremyhu):

 Apparently, upstream believes 3.4 to be the newest version of LLVM that
 supports ghc-7.8.3.  See maxSupportLlvmVersion in
 compiler/llvmGen/LlvmCodeGen/Base.hs.

 Given that ghc-7.8.3 is about 3 years old and the current release version
 is 8.2.2, can we just bump to a newer version of ghc and its supported
 version of llvm?

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Ticket URL: <https://trac.macports.org/ticket/52551#comment:11>
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