[MacPorts] #65532: isl @0.25: builds failing for 10.7 and 10.13; needs fixes for c++17 detection

[MacPorts]

#65532: isl @0.25: builds failing for 10.7 and 10.13; needs fixes for c++17
detection
-------------------------+---------------------------------
  Reporter:  dyne2meter  |      Owner:  MarcusCalhoun-Lopez
      Type:  defect      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.7.2
Resolution:              |   Keywords:
      Port:  isl         |
-------------------------+---------------------------------

Comment (by kencu):

 I installed our libcxx port on 10.7, replacing the system’s libc++.

 Lots of things worked great, but for some reason iCal was crashy with that
 setup… so I came up with macports-libcxx instead, which is also not
 perfect but leaves the system alone.

 Perhaps the iCal thing is fixable… or perhaps there will be other similar
 hiccups found in the wild….

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Ticket URL: <https://trac.macports.org/ticket/65532#comment:17>
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