Guarantee that statics have unique names

While they may have the same name within various scopes, this changes static
names to use path_pretty_name to append some hash information at the end of the
symbol. We're then guaranteed that each static has a unique NodeId, so this
NodeId is as the "hash" of the pretty name.

Closes #9188
auto merge of #9206 : alexcrichton/rust/issue-9188, r=catamorphism

While they may have the same name within various scopes, this changes static
names to use path_pretty_name to append some hash information at the end of the
symbol. We're then guaranteed that each static has a unique NodeId, so this
NodeId is as the "hash" of the pretty name.

Closes #9188