[MacPorts] #53791: llvm-4.0: update to 4.0.0

[MacPorts]

#53791: llvm-4.0: update to 4.0.0
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  Reporter:  sierkb    |      Owner:  jeremyhu
      Type:  update    |     Status:  accepted
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:
Resolution:            |   Keywords:
      Port:  llvm-4.0  |
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Comment (by jeremyhu):

 Added the patch in case you want to try it out yourself.

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Ticket URL: <https://trac.macports.org/ticket/53791#comment:4>
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