Change prefix builds to use ExternalProjects to build examples
by default. This will affect our CI which only does prefix builds.
To make it work, we have to do a few adjustments:
- look for Config files in the build-tree (before Qt is installed)
- build only one examples with only a single config,
even if Qt is a multi-config build
- install examples as part of main make install step, rather than
as part of the make step (which is the default for EPs)
- adjust CXX flags when building with MSVC to ensure we can still
use sccache and separate debug info
- derive the correct install prefix for each example and pass it
to the ExternalProject
As a drive-by, add TODOs to address tidiness of the code and corner
cases that likely don't work (Conan).
Amends d97fd7af2b
Pick-to: 6.2 6.3
Task-number: QTBUG-90820
Task-number: QTBUG-96232
Change-Id: I3060da5dc64e7b06052f9dcb720d4d250f876450
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>
98c89c8cc1