[Ninja/ManifestLoader] Add initial support for an include stack, not used yet.
[Ninja/ManifestLoader] Add initial support for an include stack, not used yet.


apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild