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

[MacPorts]

#40656: Use -isystem instead of -I in default configure.cppflags
---------------------------+--------------------------------
  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:                |
---------------------------+--------------------------------

Comment (by raimue@…):

 As I said earlier the behavior we want would be the environemnt variable
 CPATH:

 {{{
 CPATH specifies a list of directories to be searched as if specified with
 -I, but after any paths given with -I options on the command line.
 }}}

 The only catch is that old clang versions do not support it and I can't
 remember which (Apple) clang version introduced it. 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.

-- 
Ticket URL: <https://trac.macports.org/ticket/40656#comment:14>
MacPorts <http://www.macports.org/>
Ports system for OS X