[MacPorts] #49792: upgrade xcode on yosemite buildbot builder tenten-slave to 6.4

[MacPorts]

#49792: upgrade xcode on yosemite buildbot builder tenten-slave to 6.4
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 Reporter:  ryandesign@…    |      Owner:  admin@…
     Type:  enhancement     |     Status:  new
 Priority:  Normal          |  Milestone:
Component:  server/hosting  |    Version:
 Keywords:                  |       Port:
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 xcode on the yosemite buildbot builder tenten-slave is currently 6.1.1. it
 should be upgraded to 6.4. the command line developer tools need to be
 updated at the same time.

 xcode 7 is available, but just in case there are any lingering problems
 with some ports due to xcode 7 not including the 10.10 sdk, we should hold
 off on upgrading to xcode 7 on the builder for now.

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Ticket URL: <https://trac.macports.org/ticket/49792>
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