[MacPorts] #59429: ocaml: Update to 4.12.0 and fix livecheck

[MacPorts]

#59429: ocaml: Update to 4.12.0 and fix livecheck
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  Reporter:  ryandesign  |      Owner:  pmetzger
      Type:  update      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  ocaml       |
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Comment (by pmetzger):

 I've updated ocaml to 4.12.0, along with some (but not all) of the
 associated machinery needed. I'm not closing this yet as a reminder that
 not everything is yet okay.

 Unfortunately I can't check on my own that 4.12.0 works properly on Apple
 Silicon; build reports solicited.

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Ticket URL: <https://trac.macports.org/ticket/59429#comment:11>
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