[MacPorts] #62688: Increase minimum C11 compatible compiler

[MacPorts]

#62688: Increase minimum C11 compatible compiler
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  Reporter:  ryandesign  |      Owner:  (none)
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  base        |    Version:  2.6.99
Resolution:              |   Keywords:
      Port:              |
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Comment (by chrstphrchvz):

 Note that there are some ports which claim statomic.h is available as of
 Xcode clang 602 (Xcode 6.3) rather than Xcode clang 700 (Xcode 7.0).

 One alternative might be to add additional options
 `compiler.requires_stdatomic_h` etc. (similar to
 `compiler.thread_local_storage`) to further restrict compiler selection.
 I‘m not certain this would be less total work to maintain, and
 awareness/adoption of it (among other things documented at
 wiki:CompilerSelection) likely depends on port maintainers’ awareness.

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Ticket URL: <https://trac.macports.org/ticket/62688#comment:2>
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