Ninja: Make cmcldeps depfile output more consistent with 'ninja -t msvc'

Ninja relies on the generator to produce paths that match up with the
paths used in the build.ninja file, which are spelled with backslashes.
Therefore, cmcldeps should canonicalize depfile paths to use backslashes
and relativize paths to the build directory.
Ninja: Update BuildDepends test to verify cmcldeps depfiles.
Merge topic 'ninja_bad_cmcldeps_paths' into next

9275554 Ninja: Update BuildDepends test to verify cmcldeps depfiles.
6fa9d0a Ninja: Make cmcldeps depfile output more consistent with 'ninja -t msvc'