Ensure that edge outputs are >= their newest input

Otherwise they'll be dirty again during the next build. So they either
need to update their timestamps, or be marked with restat so that they
won't be considered dirty again.

Test: ninja_tests (run by build-prebuilts.sh)
Change-Id: Ie004cca58735f6576e1e2ea7a126dca6992e6eaf
6 files changed