This is useful information for people that want to use Qt in their
project with CMake.
Unfortunately there is no good way to actually set
CMAKE_OSX_DEPLOYMENT_TARGET automatically with the Qt provided value,
because it needs to be set before the first project() call in a
CMake project.
This means it can be set either on the command line, or manually by the
application developer in CMakeLists.txt before the first project()
call or via a CMake toolchain.
In Qt 6 we provide a CMake toolchain file with the deployment target
already set, so if the application developer uses the Qt generated
toolchain, they will get the value automatically.
In Qt 5 the value can only be read for informational purposes only,
from the QT_DARWIN_MIN_DEPLOYMENT_TARGET property on the
Qt5::Core target. The same property is set in Qt 6 for compatibility
resons.
Task-number: QTBUG-76167
Task-number: QTCREATORBUG-22466
Pick-to: 5.15
Change-Id: Id61d70dc9a1b7a0e7cdb90b1e679171ea178126b
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
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