* Additional changes to make the tarball commitable.
- Add an empty file so an empty packages/prebuilt directory is not removed (NuGet depends on all file sources existing even if empty).
- Use version of source-build-externals with fix for patching in a broken git repo.
- Delete `objects` directory from submodule .gitdirs.
* Enable work-tree and unsafe-paths for repo-level patches to be able to apply in the checked-in tarball.
* Update src/SourceBuild/tarball/patches/nuget-client/0001-Enable-work-tree-and-unsafe-paths-to-be-able-to-appl.patch
Co-authored-by: Michael Simons <msimons@microsoft.com>
