The "all" target defined for a subdirectory (e.g. `cd sub; make` or
`ninja sub/all`) should not include the "all" targets from nested
subdirectories (e.g. `sub/sub`) that are marked as `EXCLUDE_FROM_ALL`.
Fix this and add a test case.

Issue: #19753
Co-Author: Sebastian Holtermann <sebholt@xwmw.org>