[MacPorts] #54289: libcxx{,-abi} : upgrade + "runtime" variant

[MacPorts]

#54289: libcxx{,-abi} : upgrade + "runtime" variant
-------------------------------+----------------------
  Reporter:  RJVB              |      Owner:  jeremyhu
      Type:  update            |     Status:  assigned
  Priority:  Normal            |  Milestone:
 Component:  ports             |    Version:
Resolution:                    |   Keywords:  haspatch
      Port:  libcxxabi libcxx  |
-------------------------------+----------------------

Comment (by potmj):

 Replying to [comment:8 RJVB]:

 > Interesting question: is libc++ built with GCC and itself depending on
 libstdc++ (instead of libc++abi, as on Linux) a viable candidate for the
 libc++ conversion?

 It looks like it.  I guess the whole idea of bootstrapping is to provide a
 path to clang from gcc, as indicated by: `Warning: All compilers are
 either blacklisted or unavailable; defaulting to first fallback option`.
 Somehow `libstdc++` is not included (needed) - clever stuff I guess.
 {{{
 otool -L /usr/lib/libc++.1.dylib
 /usr/lib/libc++.1.dylib:
         /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current
 version 5.0.1)
         /usr/lib/libc++abi.dylib (compatibility version 1.0.0, current
 version 5.0.1)
         /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current
 version 111.1.7)
         /usr/lib/libgcc_s.1.dylib (compatibility version 1.0.0, current
 version 1.0.0)
 otool -L /usr/lib/libc++abi.dylib
 /usr/lib/libc++abi.dylib:
         /usr/lib/libc++abi.dylib (compatibility version 1.0.0, current
 version 5.0.1)
         /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current
 version 111.1.7)
 }}}
 With the advantage that the old Xcode gcc can generate ppc i386 x86_64
 universals that work eveywhere.

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Ticket URL: <https://trac.macports.org/ticket/54289#comment:11>
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