[MacPorts] #55991: esmf: Add clang variants

[MacPorts]

#55991: esmf: Add clang variants
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  Reporter:  platipodium  |      Owner:  tenomoto
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  esmf         |
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Comment (by ryandesign):

 Can you explain why offering these variants here would be desired? Ports
 usually do not offer variants for choosing a version of clang; MacPorts
 base chooses for you.

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Ticket URL: <https://trac.macports.org/ticket/55991#comment:7>
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