[MacPorts] #59113: gcc: cannot find systems headers with Xcode 11

[MacPorts]

#59113: gcc: cannot find systems headers with Xcode 11
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  Reporter:  abyrvalk        |      Owner:  (none)
      Type:  defect          |     Status:  new
  Priority:  Normal          |  Milestone:
 Component:  ports           |    Version:
Resolution:                  |   Keywords:
      Port:  gcc7 gcc8 gcc9  |
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Comment (by mouse07410):

 Hardcoding the path was not the smartest decision, but removing the SDK
 isn't the best one either.

 And I haven't started yet on the sudden inability of Xcode to login to
 Enterprise GitHub (and often - to GitHub.com itself). Somehow, what worked
 up until Xcode-10.1 (SSH and HTTPS access) doesn't work any more (broke in
 Xcode-10.2.1, and became hopeless in Xcode-11). Regardless of what
 password of access token you pass to Xcode, or what SSH key you point it
 at - it fails to access the repos. Thankfully, there's IntelliJ IDEA and
 CLion, who have absolutely no problem connecting to all those sites with
 exactly the credentials that Xcode now fails. Go figure.

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Ticket URL: <https://trac.macports.org/ticket/59113#comment:27>
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