[MacPorts] #59108: mercurial 5.1: fails to build with "ld: library not found for -lSystem"

[MacPorts]

#59108: mercurial 5.1: fails to build with "ld: library not found for -lSystem"
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  Reporter:  ylluminarious  |      Owner:  (none)
      Type:  defect         |     Status:  new
  Priority:  Normal         |  Milestone:
 Component:  ports          |    Version:  2.6.0
Resolution:                 |   Keywords:
      Port:  mercurial      |
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Comment (by ryandesign):

 Well, the log shows you're using Xcode 11, yet the build is using flags
 like
 `-Wl,-syslibroot,/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk`.
 Xcode 11 does not contain the 10.14 SDK; it only contains the 10.15 SDK.
 There are many other tickets for this issue already.

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Ticket URL: <https://trac.macports.org/ticket/59108#comment:2>
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