If a prereq of a pattern is explicitly mentioned as a prereq of an
unrelated rule, it should not be considered an intermediate file.
* tests/scripts/features/double_colon: Add tests mentioning unrelated
explicit targets.
* tests/scripts/features/grouped_targets: Ditto.
* tests/scripts/features/implicit_search: Ditto.
* tests/scripts/features/patternrules: Ditto.
* tests/scripts/features/se_implicit: Ditto.
* tests/scripts/features/statipattrules: Ditto.