Merge topic 'autogen-enable-depfiles'

680fbb112a Autogen: Enable depfile support for Visual Studio and Xcode generators
d9f569c246 Autogen: Skip per-compilation dep reading when depfile merge is used

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !11844