[MacPorts] #64088: cargo-c fails to build on 10.13

[MacPorts]

#64088: cargo-c fails to build on 10.13
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  Reporter:  bK4gYuRo  |      Owner:  MarcusCalhoun-Lopez
      Type:  defect    |     Status:  assigned
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:  2.7.1
Resolution:            |   Keywords:  cargo-c
      Port:  cargo-c   |
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Comment (by mascguy):

 Replying to [comment:15 bK4gYuRo]:
 > {{{sudo port rev-upgrade}}} comes up clean, {{{sudo port diagnose}}}
 yields nothing. {{{sudo port install cargo-c}}} fails with the same errors
 in the main.log. To make sure we are comparing apples to apples, what is
 your version of XCode that succeeds to build cargo-c? Mine is 9.4.1. Also,
 if it is relevant, I have rustc 1.56.1.

 Presently I'm building with Xcode 10.1. But I'll switch to 9.4.1, and
 rebuild with that. More to follow.

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Ticket URL: <https://trac.macports.org/ticket/64088#comment:16>
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