[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
Resolution:               |   Keywords:
      Port:               |
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Comment (by kencu):

 So - you'll notice that this forces all these systems 10.6 through 10.8 to
 basically build everything with clang-5.0. I just can't help but think
 this makes a lot of sense, removes our need to set up complicated compiler
 floors with certain c++ or C standard support available, and makes all
 these systems build with basically the same compiler that newer systems
 use (and are tested against, etc).

 I realize that means that clang-5.0 will need to be called in for every
 build on these systems. But I submit that is a better option than the
 alternative of seeing builds fail with older builds of clang, and forcing
 them all up to something newer.

 All these systems will end up with clang-5.0 anyway, for some port or
 another.

 And it allow the default -stdlib to be set to libc++ on clang-5.0, and
 have this carry through to all these older systems.

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Ticket URL: <https://trac.macports.org/ticket/56041#comment:3>
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