fail some build steps if changed or unversioned files exist at the end / several related cleanups and adjustments

[firewave]

No description provided.

[firewave]

This is to expose tests (or other commands) which generate (and leave) files in the source tree. Files which are being ignored should not fail this.

This should primarily be fixed by using temporary folders. In case this can't be done we need to make sure they are cleaned up - and in some cases we might also need to clean previously existing files beforehand.

[firewave]

HEAD detached at pull/6787/merge
Untracked files:
(use "git add <file>..." to include in what will be committed)
.ccache/
addons/test/cppcheck-addon-ctu-file-list
cmake.output.signal/
cppcheck-addon-ctu-file-list
test-signalhandler
test-stacktrace
test/cli/cppcheck-addon-ctu-file-list
test/cli/helloworld/cppcheck-addon-ctu-file-list
test/cli/helloworld/test.cppcheck
test/cli/proj2/test.cppcheck
test/cli/test.cppcheck
nothing added to commit but untracked files present (use "git add" to track)