make: better determine that a file is up-to-date

POSIX says:

   A target shall be considered up-to-date... if it has already
   been made up-to-date by the current invocation of make
   (regardless of the target's existence or age).

   If the target does not exist after the target has been
   successfully made up-to-date, the target shall be treated as
   being newer than any target for which it is a prerequisite.

Previously 'make' assumed that if a rule had succeeded the
modification time of the target would be the current time.  This
isn't necessarily the case.  Instead:

- If the file exists use the modification time of the file as the
  the time of the target.

- If it doesn't exist use the current time, which should be more
  recent than the time of any file for which it's a prerequisite.

Adds 16 bytes.

(GitHub issue #410)

0 files changed, 0 insertions, 0 deletions