[MacPorts] #69805: macports-libcxx: sync with the latest compatible version of LLVM

[MacPorts]

#69805: macports-libcxx: sync with the latest compatible version of LLVM
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  Reporter:  aeiouaeiouaeiouaeiouaeiouaeiou  |      Owner:  (none)
      Type:  defect                          |     Status:  new
  Priority:  Normal                          |  Milestone:
 Component:  ports                           |    Version:
Resolution:                                  |   Keywords:
      Port:  macports-libcxx, bitcoin        |
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Comment (by kencu):

 just a heads-up that libcxx makes no attempt to maintain compatibility
 between versions. Requests to upstream to maintain object layouts to
 maintain compatibilty between libcxx versions have been declined — it’s
 not something they want to have to support.

 I chose the libcxx from clang-11 to be the one used in macports-libcxx so
 as to try to be the most compatible with the libcxx installed in the
 system on the needed systems.

 When/if macports-libcxx is inevitably updated, it is quite possible more
 ABI incompatibilities might creep in, much like what happened with gcc and
 libstdc++. Some testing will be needed. We have seen a few minor ABI
 issues already using the macports-libcxx we have, but all-in it’s been
 more successful than I had expected. That might change.

-- 
Ticket URL: <https://trac.macports.org/ticket/69805#comment:3>
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