[MacPorts] #61458: fresh install on Big Sur emits warning about SDK not installed

[MacPorts]

#61458: fresh install on Big Sur emits warning about SDK not installed
---------------------+--------------------
  Reporter:  wlipa   |      Owner:  (none)
      Type:  defect  |     Status:  new
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:  2.6.4
Resolution:          |   Keywords:
      Port:          |
---------------------+--------------------

Comment (by wlipa):

 Xcode seems to think it's there:


 {{{
 $ xcodebuild -showsdks
 iOS SDKs:
         iOS 14.2                        -sdk iphoneos14.2

 iOS Simulator SDKs:
         Simulator - iOS 14.2            -sdk iphonesimulator14.2

 macOS SDKs:
         DriverKit 20.0                  -sdk driverkit.macosx20.0
         macOS 11.0                      -sdk macosx11.0

 tvOS SDKs:
         tvOS 14.2                       -sdk appletvos14.2

 tvOS Simulator SDKs:
         Simulator - tvOS 14.2           -sdk appletvsimulator14.2

 watchOS SDKs:
         watchOS 7.1                     -sdk watchos7.1

 watchOS Simulator SDKs:
         Simulator - watchOS 7.1         -sdk watchsimulator7.1


 }}}

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Ticket URL: <https://trac.macports.org/ticket/61458#comment:1>
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