[SV 63098] Enhance detection of missing peer also-make targets

[SV 63098] Enhance detection of missing peer also-make targets

The previous attempt to detect missing peer targets for implicit
rules had some holes.  Move the detection to notice_finished_file().

* src/remake.c (check_also_make): If we don't have the current mtime
for the file, obtain it.
(update_goal_chain): Don't call check_also_make() here.
(check_dep): Ditto.
(notice_finished_file): If we finished running an implicit rule that
has also_make targets, invoke check_also_make().