[MacPorts] #20408: Move Xcode version checking code to new PortGroup

[MacPorts]

#20408: Move Xcode version checking code to new PortGroup
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 Reporter:  ryandesign@…             |       Owner:  ryandesign@…           
     Type:  enhancement              |      Status:  assigned               
 Priority:  Normal                   |   Milestone:                         
Component:  ports                    |     Version:  1.7.1                  
 Keywords:                           |        Port:                         
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Comment(by ryandesign@…):

 Attached is a diff of how this PortGroup could be used in the tiff port.

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Ticket URL: <http://trac.macports.org/ticket/20408#comment:2>
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