[MacPorts] #53605: get GCC to use libc++?

[MacPorts]

#53605: get GCC to use libc++?
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  Reporter:  RJVB         |      Owner:
      Type:  enhancement  |     Status:  new
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  gcc6 gcc7    |
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Comment (by RJVB):

 Improved version

 - adds GCC's libsupc++ (static lib) which provides a number of symbols
 missing from older libc++ versions
 - better mechanism through which libstdc++ is pulled in during the GCC
 build (it remains to be seen if it isn't better to deactivate libc++
 entirely during GCC's own build)
 - drops the symlinked llvm/c++ header directory and adds an env. variable
 to override the default, built-in llvm/c++ header directory
 - new `libcxx` variant that sets the default llvm/c++ header dir to the
 one of the default system toolchain (not a good idea on 10.9)

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Ticket URL: <https://trac.macports.org/ticket/53605#comment:8>
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