Slightly simplify .def file use. From `gn help sources`: As a special case, a file ending in ".def" will be treated as a Windows module definition file. It will be appended to the link line with a preceding "/DEF:" string. This makes the code slightly shorter, and also gives ninja a chance of re-running the link when the .def file changes since it now knows about this file. No intended behavior change. Change-Id: I5fecb22752508880b726482f7c3da5a75180e446 Reviewed-on: https://chromium-review.googlesource.com/c/1396499 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Nico Weber <thakis@chromium.org>