https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77593
--- Comment #2 from tprince at computer dot org --- I suspect the Windows 10 provided svn may be partly at fault (although it works for bootstrapping on the Microsoft provided gcc in linux subsystem). I grabbed trunk using cygwin svn and have seen the bootstrap go as far as the stage3 libstdc++ build (without intervention) before jumping back to stage1 and failing on permissions to move into stage1-gcc.
