CMake: Fix picking of the binary_for_strip project location

Fix binary_for_strip project not being found when the following
conditions were met:
- building a repo other than qtbase
- qtbase sources are not available on the machine
(usually happens in CI where only the current repo sources are
available).

The issue was that QT_CMAKE_DIR would always be defined, regardless of
which repo was being built and the system would incorrectly assume
the location of the project files.

The fix is to always pick up the sources from qtbase's source dir if
they are available (this time done with an appropriate check),
otherwise use the installed files.

Note that the behavior of always using the qtbase sources if available
is not exactly the best, but it is a more general issue that affects
other code too.
In the name of consistency, make it so for the binary_for_strip
project as well, but add TODOs in code to address the situation
in a separate change.

Amends 39f657032b5e65bfcb93472201f6607c0388ba37

Pick-to: 6.2 6.3
Fixes: QTBUG-102064
Task-number: QTBUG-88090
Task-number: QTBUG-101653
Change-Id: I0649f945e9ff0ab1f597c51bb5ab389fa665c021
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>

0 files changed, 0 insertions, 0 deletions