[MacPorts] #43762: Update arb to 6.0-rc2

[MacPorts]

#43762: Update arb to 6.0-rc2
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  Reporter:  matt.cottrell@…  |      Owner:  macports-tickets@…
      Type:  update           |     Status:  new
  Priority:  Normal           |  Milestone:
 Component:  ports            |    Version:  2.2.1
Resolution:                   |   Keywords:  haspatch maintainer
      Port:  arb              |
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Comment (by matt.cottrell@…):

 The upstream developer has now fixed a bunch of bugs related to this
 issue.   I am attaching a new Portfile.diff that should clear up the
 compiler error.

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Ticket URL: <https://trac.macports.org/ticket/43762#comment:9>
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