the new CI uses make install to collect the artifacts for use in the build of subsequent modules. this is correct for prefix builds, but not so much for non-prefix builds - which breaks https://codereview.qt-project.org/126345.
instead, the system should pack up the build dir as-is, with two exceptions:
- it's ok to filter out artifacts which are known to be useless to subsequent modules, like object files
- in non-prefix builds, all modules build into the qtbase build dir. that means that any particular module's build includes the artifacts of all its dependencies. these should be omitted as well.