Fix up test.
Merge topic 'target-transitive-sources' into next

1570aaad Fix up test.
cmTarget: Make the SOURCES origin tracable.
Make the SOURCES target property writable.
target_sources: New command to add sources to target.
Merge topic 'target-transitive-sources' into next

345e48e9 target_sources: New command to add sources to target.
e80b9fbf Make the SOURCES target property writable.
62ded28b cmTarget: Make the SOURCES origin tracable.