[MacPorts] #61921: qt5-qtwebengine @5.15.2: does not build on macOS 10.13 with Xcode 9

[MacPorts]

#61921: qt5-qtwebengine @5.15.2: does not build on macOS 10.13 with Xcode 9
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  Reporter:  dliessi          |      Owner:  (none)
      Type:  defect           |     Status:  new
  Priority:  Normal           |  Milestone:
 Component:  ports            |    Version:
Resolution:                   |   Keywords:  highsierra
      Port:  qt5-qtwebengine  |
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Comment (by kencu):

 When fixing qt5.3 for SnowLeopard, I settled on clang-9.0 as the compiler
 that would be used, and built qt5-qttools with that. As I recall that
 compiler was then baked into qt5-qttools, and was thereafter used for all
 the qt5 builds on SnowLeopard, which is what I wanted.

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Ticket URL: <https://trac.macports.org/ticket/61921#comment:5>
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