[MacPorts] #58712: clang-7.0 and clang-8.0 are missing atomic builtins on i386

[MacPorts]

#58712: clang-7.0 and clang-8.0 are missing atomic builtins on i386
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  Reporter:  devernay             |      Owner:  (none)
      Type:  defect               |     Status:  new
  Priority:  Normal               |  Milestone:
 Component:  ports                |    Version:
Resolution:                       |   Keywords:
      Port:  clang-7.0,clang-8.0  |
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Comment (by kencu):

 interesting. I guess with Apple's deprecating i386 it's up to us to fix
 this for Darwin.

 Help me understand better where x86_64 is finding these symbols; maybe we
 can fix it there?

 Otherwise...what shared library could we put it in? The only one I can
 think of that is always linked in at the moment is libSystem...

 Or, for +universal builds, we could put it back in libruntime, but that
 sorta defeats the point of the fix, I guess...

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Ticket URL: <https://trac.macports.org/ticket/58712#comment:2>
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