Submodule local/sources/relibc updated to dff28f00, which implements
two panic-site fixes found by the Round 9 stub audit:
* ld_so/linker.rs: RTLD_NOLOAD|RTLD_NOW no longer panics with
todo!(); returns already-loaded id or DlError::NotFound.
* header/dirent/mod.rs: readdir_r() no longer panics with
unimplemented!(); wraps readdir() per POSIX Issue 8.
See submodule commit message for full rationale.
vasilito
2a2d1f354c