[MacPorts] #44125: cmake: default values of CMAKE_OSX_SYSROOT/DEPLOYMENT_TARGET (prevent linking against libc++)

[MacPorts]

#44125: cmake: default values of CMAKE_OSX_SYSROOT/DEPLOYMENT_TARGET (prevent
linking against libc++)
---------------------+--------------------------
 Reporter:  mojca@…  |      Owner:  css@…
     Type:  defect   |     Status:  new
 Priority:  Normal   |  Milestone:
Component:  ports    |    Version:
 Keywords:           |       Port:  cmake libcxx
---------------------+--------------------------
 When compiling against `libc++` on 10.6 CMake fails to work because:
   * the cmake PortGroup adds
 {{{
 -DCMAKE_OSX_SYSROOT="/Developer/SDKs/MacOSX10.6.sdk" \
 -DCMAKE_OSX_DEPLOYMENT_TARGET="10.6"
 }}}
   * even if CMake PortGroup wouldn't add those variables, CMake seems to
 add `-isysroot` automatically unless the above variables are set to blank:
 {{{
 -DCMAKE_OSX_SYSROOT="/" \
 -DCMAKE_OSX_DEPLOYMENT_TARGET=""
 }}}

 This looks partially as an upstream "bug", partially as a bug in the
 portgroup, see comment:7:ticket:44062. But maybe it's considered a feature
 to help developers link against an earlier framework?

 The main question is: should this be fixed? Upstream? In MacPorts? Or not
 at all? Should we set the flags to empty perhaps (unless a different SDK
 is required)? Or maybe `libc++` should also be installed inside the SDK?

 This is likely not only an issue with `libc++`. `libc++` is just an
 example that was affected.

-- 
Ticket URL: <https://trac.macports.org/ticket/44125>
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