[MacPorts] #61580: libdv @1.0.0 build failure with Xcode 12

[MacPorts]

#61580: libdv @1.0.0 build failure with Xcode 12
-----------------------------+-----------------------------
  Reporter:  MaurizioLoreti  |      Owner:  ryandesign
      Type:  defect          |     Status:  accepted
  Priority:  Normal          |  Milestone:
 Component:  ports           |    Version:
Resolution:                  |   Keywords:  bigsur catalina
      Port:  libdv           |
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Comment (by ryandesign):

 Initially the patch didn't work for me: it adds a configure test for
 `sched_setscheduler` but it surprisingly determined that it was available,
 and then the build failed as before.

 I noticed that the port forces the use of `-flat_namespace -undefined
 suppress` which has been in the port ever since it was added in 2005 in
 [8ed1835344effbeda34c7df31fce834174521fcf/macports-ports]. That was right
 after the release of Mac OS X 10.3. The use of the flat namespace was
 typical on Mac OS X 10.2 and earlier but in 10.3 and later the two-level
 namespace should be used instead. After removing the lines that forced the
 flat namespace, the configure test correctly determines that
 `sched_setscheduler` doesn't exist and the build succeeds.

-- 
Ticket URL: <https://trac.macports.org/ticket/61580#comment:5>
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