win_toolchain: Write json files only if different from what is on disk
win_toolchain: Write json files only if different from what is on disk

Bug: chromium:1188672
Change-Id: I10aed281afd636acc0c680a7da486ae74aa637df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2807968
Auto-Submit: Nico Weber <c0f02d98506190746d1cdcb01be0f37b51e27077@chromium.org>
Commit-Queue: Bruce Dawson <fe9e26f3989304bf7275ed139c57fd059c63d22d@chromium.org>
Reviewed-by: Bruce Dawson <fe9e26f3989304bf7275ed139c57fd059c63d22d@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools