Auto merge of #9814 - ehuss:move-tmp, r=alexcrichton
Move `tmp` test directory.
The `tmp` directory added in #9375 was placed within the profile directory (such as `target/debug/tmp` or `target/release/tmp`). This causes problems for any cargo target (binary, test, etc.) with the name `tmp` as there is a name collision. This PR attempts to address that by moving the `tmp` directory to the root of the target directory (`target/tmp`), and reserving the profile name "tmp".