[MacPorts] #58653: Some portfiles fail to parse under linux

[MacPorts]

#58653: Some portfiles fail to parse under linux
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  Reporter:  mojca                               |      Owner:  (none)
      Type:  defect                              |     Status:  new
  Priority:  Normal                              |  Milestone:
 Component:  ports                               |    Version:
Resolution:                                      |   Keywords:
      Port:  botan chicken fpc gnuradio macos-   |
  vpn-server mlt octave psi py-eric-ide qt4-mac  |
  texworks wireshark22                           |
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Comment (by mojca):

 I agree that we should fix the Qt4 PortGroup to not raise a parse error. I
 also realized that we probably have a global problem of using
 `${os.major}` checks all over the place to do some conditional checks on
 macOS version number, and I assume this would also affect Linux in strange
 ways. If a port only works on 10.13 and newer, the "if" statement checking
 for `${os.major}` being high enough would probably evaluate to false on
 Linux.

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Ticket URL: <https://trac.macports.org/ticket/58653#comment:12>
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