Auto merge of #53762 - flip1995:tool_lints, r=Manishearth

Backwards compatibility for tool/clippy lints

cc #44690
cc https://github.com/rust-lang-nursery/rust-clippy/pull/2977#issuecomment-409706557

This is the next step towards `tool_lints`.

This makes Clippy lints still work without scoping, but will warn and suggest the new scoped name. This warning will only appear if the code is checked with Clippy itself.

There is still an issue with using the old lint name in inner attributes. For inner attributes the warning gets emitted twice. I'm currently not really sure why this happens, but will try to fix this ASAP.

r? @Manishearth