[MacPorts] #27199: libxml2: update to 2.7.8

[MacPorts]

#27199: libxml2: update to 2.7.8
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 Reporter:  jmr@…             |       Owner:  cedric.luthi@…        
     Type:  update            |      Status:  new                   
 Priority:  Normal            |   Milestone:                        
Component:  ports             |     Version:                        
 Keywords:  haspatch          |        Port:  libxml2               
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 Patch attached.

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Ticket URL: <https://trac.macports.org/ticket/27199>
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