The [build] exclude list names platforms (OS cascade entries) on which a
project's build is excluded, not projects. pkg_relations() implements
--skip-excluded by walking the seeds' exclude values as if they were
project specs, so a value such as "debian" is visited as a project, the
installed-package check fails with "Unmet dependency on debian: the -run
package of project debian is not installed", and `make
pkg-install-testbuild-deps` breaks.
Implement the flag's documented semantics using
App.is_excluded_from_build(): an excluded seed is neither considered nor
output, an excluded module in the dependency closure contributes no
dependencies, and excluded modules are not output as jw dependencies. This
matches what required-os-pkg already does.
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.87.0
Signed-off-by: Jan Lindemann <jan@janware.com>