Update compiler-rt

Closes #12356
auto merge of #12359 : alexcrichton/rust/update-compiler-rt, r=luqmana

Closes #12356
Make priavcy checking aware that a `use` directive can point to two defintions (namespaces) with different privacy. Closes #4110
auto merge of #12245 : nick29581/rust/priv2, r=alexcrichton

closes #4110