[MacPorts] #67724: mpich: enable F08 when updating

[MacPorts]

#67724: mpich: enable F08 when updating
---------------------------+----------------------
  Reporter:  barracuda156  |      Owner:  mascguy
      Type:  defect        |     Status:  assigned
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:  2.8.1
Resolution:                |   Keywords:
      Port:  mpich         |
---------------------------+----------------------

Comment (by barracuda156):

 Just for the record, I have just built `mpich` with `gcc13`.

 {{{
 36-125% port -v installed mpich-gcc13
 The following ports are currently installed:
   mpich-gcc13 @4.1.2_0+fortran (active) requested_variants=''
 platform='darwin 10' archs='ppc' date='2023-10-08T01:28:48+0800'
 }}}

 P. S. These are also unneeded now: `"F90FLAGS='' F90=''"`, I dropped
 those.

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Ticket URL: <https://trac.macports.org/ticket/67724#comment:15>
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