[MacPorts] #59088: Xcode update broke linkages

[MacPorts]

#59088: Xcode update broke linkages
---------------------+---------------------
  Reporter:  rhc54   |      Owner:  (none)
      Type:  defect  |     Status:  new
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:  2.6.0
Resolution:          |   Keywords:  xcode11
      Port:          |
---------------------+---------------------

Comment (by ryandesign):

 Well, Apple has been doing this for years—releasing a new major version of
 Xcode that only contains the SDK for the then-most-recent version of
 macOS, even if that is later than the version of macOS you're running
 Xcode on. And this has not been a problem.

 Xcode 11 is the first time this is causing a problem for us, because prior
 to macOS Mojave the command line tools provided headers that matched the
 OS version in /usr/include and we just used those. As of Mojave, that's no
 longer the case, so we had to use the SDK path. At the time, with Xcode
 10, that was the 10.14 SDK path. Now that Xcode 11 is out, which doesn't
 have a 10.14 SDK, we're discovering all the places where the SDK path got
 baked into programs. It's the same problem I discovered years ago when
 investigating whether we should make MacPorts always use the SDK; see
 #41783.

 I agree that if we used the unversioned MacOSX.sdk we would not have as
 bad a problem, and maybe that's what we should modify MacPorts base to do,
 though that still comes with the problem that it is specific to the Xcode
 installation directory, and thus requires that Xcode exists and is in its
 default location. Meanwhile effort has been put into allowing MacPorts to
 function better without needing Xcode to be installed; baking Xcode-
 relative SDK paths into programs defeats that.

 I don't know of a solution that covers all bases.

-- 
Ticket URL: <https://trac.macports.org/ticket/59088#comment:9>
MacPorts <https://www.macports.org/>
Ports system for macOS