Windows pre-built nativelink v5 (1.6.6 + directory-cache junction mode)

nativelink.exe from branch v1.6.6-windows at 8c4da49: upstream v1.6.6, the absolute-path fix for canonicalise_path, and the experimental directory-cache junction mode (experimental_junction_paths, anchored at the input root). Cross-compiled from Linux with cargo-xwin.