If a prereq of a pattern is an explicit target, it should not be
considered an intermediate file.
(Minor tweaks by Paul Smith <psmith@gnu.org>)
* src/dep.h (struct nameseq): Add is_explicit flag.
* src/implicit.c (struct patdeps): Ditto.
(pattern_search): Set the is_explicit flag appropriately for each
prerequisite, based on whether it contained a pattern or not.
Update the help output to note implicit vs. explicit prereqs.
* tests/scripts/features/double_colon: Add tests.
* tests/scripts/features/grouped_targets: Ditto.
* tests/scripts/features/patternrules: Ditto.
* tests/scripts/features/se_implicit: Ditto.
* tests/scripts/features/statipattrules: Ditto.