[MacPorts] #56041: Update compiler selection for 10.6-10.8 with libc++

[MacPorts]

#56041: Update compiler selection for 10.6-10.8 with libc++
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 Reporter:  jmroot       |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:  MacPorts 2.5.0
Component:  base         |    Version:  2.4.2
 Keywords:               |       Port:
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 For this configuration on these systems, we need to at least default
 configure.cxx to a compiler that can use libc++. We probably also need
 some bootstrap (libstdc++ using) versions of toolchain ports so that the
 manual intervention described in LibcxxOnOlderSystems is not required.

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Ticket URL: <https://trac.macports.org/ticket/56041>
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