[MacPorts] #40656: Use -isystem instead of -I in default configure.cppflags

[MacPorts]

#40656: Use -isystem instead of -I in default configure.cppflags
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  Reporter:  ryandesign@…  |      Owner:  macports-tickets@…
      Type:  enhancement   |     Status:  closed
  Priority:  Normal        |  Milestone:  MacPorts Future
 Component:  base          |    Version:  2.2.0
Resolution:  fixed         |   Keywords:  haspatch
      Port:                |
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Comment (by ryandesign@…):

 Replying to [comment:14 raimue@…]:
 > I propose we switch to CPATH when using Xcode >= 5. That version would
 definitely be new enough and required for both our currently supported
 platforms. Same for LIBRARY_PATH.

 MacPorts already sets CPATH and LIBRARY_PATH in all phases and has done so
 for years.

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Ticket URL: <https://trac.macports.org/ticket/40656#comment:15>
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