Merge c4d4731b: 'Build SDK repository'. Do not merge.

When the build is invoked with the fake target "sdk_repo" and
a main target of sdk, win_sdk or sdk_addon, we now create
packages in DIST_DIR that can directly be used to populate the
SDK Repository.
This is quite close to how we actually distribute the SDK.

Change-Id: I863ac8baf159432d7c95df46cba6e4f3b9122629