[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 jmr@…):

 So this breaks some things that parse flags and don’t know about -isystem,
 right? Specifically swig, which is used kind of a lot.

 https://lists.macosforge.org/pipermail/macports-
 dev/2014-January/025753.html

 Can we please revert this and clear or change configure.cppflags in only
 the ports that need it, or if you don’t care about old clang as per
 comment:10 just don’t set CPPFLAGS to anything by default, and reply on
 CPATH?

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Ticket URL: <https://trac.macports.org/ticket/40656#comment:16>
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