[MacPorts] #56669: ldns 1.7.0 ./configure fails to find the SDK on MacOS X <= 10.6

[MacPorts]

#56669: ldns 1.7.0 ./configure fails to find the SDK on MacOS X <= 10.6
-------------------------------+--------------------
 Reporter:  grumpybozo         |      Owner:  (none)
     Type:  defect             |     Status:  new
 Priority:  Normal             |  Milestone:
Component:  ports              |    Version:  2.5.2
 Keywords:  haspatch upstream  |       Port:  ldns
-------------------------------+--------------------
 The root cause is reliance on "xcrun --show-sdk-version" to identify the
 proper SDK version. The "--show-sdk-version" option did not exist in the
 xcrun utility until MacOS X 10.7 (XCode 4.)

 The attached patch to configure.ac fixes (after running autoreconf) this
 problem for MacOS X 10.6. I have submitted it upstream as well:
 https://www.nlnetlabs.nl/bugs-script/show_bug.cgi?id=4105

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Ticket URL: <https://trac.macports.org/ticket/56669>
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