[MacPorts] #34287: update petsc Portfile to include external software

[MacPorts]

#34287: update petsc Portfile to include external software
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 Reporter:  christophe.prudhomme@…                |       Owner:  macports-tickets@…                   
     Type:  enhancement                           |      Status:  new                                  
 Priority:  Normal                                |   Milestone:                                       
Component:  ports                                 |     Version:  2.0.4                                
 Keywords:                                        |        Port:  petsc                                
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 This patch allows to install along side petsc several libraries providing:
  - direct solvers (sequential : umfpack and sequential/parallel: mumps)
  - partitioner : scotch, parmetis
  - multi grid solver (ml)
  - blacs/scalapack support (required by mumps)

 these external libraries are installed in $PETSC_DIR

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Ticket URL: <https://trac.macports.org/ticket/34287>
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