[MacPorts] #57875: port:poppler shouldn't require C++14?!

[MacPorts]

#57875: port:poppler shouldn't require C++14?!
----------------------+----------------------
  Reporter:  RJVB     |      Owner:  dbevans
      Type:  defect   |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:
Resolution:           |   Keywords:
      Port:  poppler  |
----------------------+----------------------

Comment (by RJVB):

 Indeed, the changelog suggests as much. Curious that clang 5 accepts it
 when set to use C++11 then but whatever, maybe a snippet like below can be
 useful (adapted where necessary; I might still have clang 4 installed
 myself for instance to see if that version works):

 {{{
 foreach clv {3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0} {
     compiler.blacklist macports-clang-${clv}
 }
 foreach clv {5.0 6.0 7.0} {
     if {[file exists ${prefix}/bin/clang-mp-${clv}]} {
         compiler.whitelist-prepend macports-clang-${clv}
     }
     compiler.fallback-prepend macports-clang-${clv}
 }
 }}}

 Without that my build attempt on 10.9.5 where I didn't specify a compiler
 picked the Xcode 6.2 clang version (AppleClang 6.x) which rather evidently
 failed (on thread_local) so the current blacklist formula isn't enough.
 The snippet above has the effect that the newest MacPorts clang version
 that the user has installed (from 5, 6 or 7) will be selected for building
 (seems like the obvious thing to do but yet "base" doesn't).

 FWIW, poppler is a port that is used by a number of valuable utilities, so
 we should take reasonable measures to keep it building on platforms where
 C++14 support isn't so good. CPPPreference provides a possible
 std::make_unique implementation that works under C++11 which maybe we
 could inject if necessary.

-- 
Ticket URL: <https://trac.macports.org/ticket/57875#comment:4>
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