rust private

rustbuild: Fix `no output generated` error for next bootstrap cargo. Due to rust-lang/cargo#4570, a `*.dll.lib` file is uplifted when building dynamic libraries on Windows. The current bootstrap code does not understand files with multiple extensions, and will instead assume `xxxx.dll` is the file name. This caused a `no output generated` error because it tries to search for `xxxx.dll-hash.lib` inside the `deps/` folder, while it should check for `xxxx-hash.dll.lib` instead. This PR is blocking #45285, see https://github.com/rust-lang/rust/pull/45285#issuecomment-338454149 and the rest of the comments for detail.