[MacPorts] #52468: gtk3 3.22.0_0 build fails on 10.5 ppc

[MacPorts]

#52468: gtk3 3.22.0_0 build fails on 10.5 ppc
-----------------------+-----------------------------
  Reporter:  dgonyier  |      Owner:  dbevans
      Type:  defect    |     Status:  assigned
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:  2.3.4
Resolution:            |   Keywords:  leopard powerpc
      Port:  gtk3      |
-----------------------+-----------------------------

Comment (by kencu):

 Adding `PortGroup cxx11 1.1` and removing the other blacklisting would now
 appear to be the most appropriate way to solve the toolchain issues in
 this ticket. Works fine on 10.4 and 10.5 PPC using gcc6, and provides the
 clang version minimums previously indicated in the Portfile for the Intel
 builds.

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Ticket URL: <https://trac.macports.org/ticket/52468#comment:60>
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