Certain platform-related variables, in this case UNIX, must be set in a
platform module, because they get cleared after the toolchain file is
loaded. Such platform modules live in upstream CMake, but there is none
yet for INTEGRITY. This manifests in an undefined UNIX variable and
"System is unknown to CMake" warnings for the project and every
configure test.
Add the CMake module "Platform/Integrity" in the cmake/platforms
directory. Add this directory to CMAKE_MODULE_PATH to let CMake load
Platform/Integrity when the toolchain file set CMAKE_SYSTEM_NAME to
"Integrity".
CMake's module directory takes precedence, when loading platform
modules. This is special for platform modules and different from the
documented behavior of CMAKE_MODULE_PATH and include().
In case the user wants to provide their own platform modules via
CMAKE_MODULE_PATH, they can instruct Qt to not add its path by setting
QT_AVOID_CUSTOM_PLATFORM_MODULES to ON.
Make sure that configure tests with project files also load the custom
platform module.
Pick-to: 6.2
Fixes: QTBUG-96998
Change-Id: I9855d620d24dc66353cec5e847a2675b464ace26
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
