[MacPorts] #53617: isl: Update to 0.18

[MacPorts]

#53617: isl: Update to 0.18
-------------------------+---------------------------------
  Reporter:  ryandesign  |      Owner:  MarcusCalhoun-Lopez
      Type:  update      |     Status:  closed
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:  fixed       |   Keywords:
      Port:  isl         |
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Comment (by mojca):

 This broke gcc48. See #53662.

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Ticket URL: <https://trac.macports.org/ticket/53617#comment:3>
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