[MacPorts] #55709: libcxx @5.0.1_1 build fails with gcc

[MacPorts]

#55709: libcxx @5.0.1_1 build fails with gcc
---------------------+-------------------------------
  Reporter:  potmj   |      Owner:  jeremyhu
      Type:  defect  |     Status:  assigned
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:  2.4.2
Resolution:          |   Keywords:  leopard universal
      Port:  libcxx  |
---------------------+-------------------------------

Comment (by RJVB):

 I'm trying to help our potmj with his bootstrapping problem, not trying to
 tell MacPorts or Jeremy what to do.

 But FWIW, port:cmake could easily provide a version not requiring C++11 on
 platforms where this is appropriate.

 > Just because his universal_archs are set to i386 x86_64 doesn't mean he
 will have to build everything universal.

 Yet this is what will happen unless you add `-universal` each time you
 don't want it, and most ports are not available as universal binary
 builds. Even installing the "wrong" port `+universal` means you can end up
 with all dependencies installed that way too, including big ones like
 clang.

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Ticket URL: <https://trac.macports.org/ticket/55709#comment:8>
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