[MacPorts] #43704: unify the use of +threads as a variant name

[MacPorts]

#43704: unify the use of +threads as a variant name
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  Reporter:  mojca                             |      Owner:  macports-
                                               |  tickets@…
      Type:  enhancement                       |     Status:  new
  Priority:  Normal                            |  Milestone:
 Component:  ports                             |    Version:
Resolution:                                    |   Keywords:
      Port:  boost cherokee gauche hdf5 raxml  |
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Comment (by michaelld):

 OK. So for "boost" by default we install just the multi-threaded version
 (suffix "-mt"). IIRC, disabling the default "+no_single" will then -also-
 build a single-threaded version (suffix "-st") ... completely different
 ABI files. I don't see how "+threads" is relevant here.

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Ticket URL: <https://trac.macports.org/ticket/43704#comment:8>
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