[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 barracuda156):

 > You'll have to dig in on why 10.8 builds but 10.7 doesn't, but I would
 guess 10.8 uses the system compiler which tests as having no c++17
 support, whereas 10.7 uses clang-14 which seems to support c++17, but in
 the end, the overall system does not support it well enough and the link
 fails.

 It also builds fine on 10.6.

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Ticket URL: <https://trac.macports.org/ticket/65532#comment:14>
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