[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 platipodium):

 There is no need for a specific version of clang.  I am fine with ports
 choosing this for me.  But currently, clang is expressedly *excluded*.
 This is a defect, as there   is a designated version of ESMF (denoted
 gfortranclang) that compiles the C++ part of ESMF with clang and the
 fortran part with gfortran.  This is currently not possible with mac
 ports.

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Ticket URL: <https://trac.macports.org/ticket/55991#comment:8>
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