This was done in #145740 and #145947. It is causing problems for people
using r-a on anything that uses the rustc-dev rustup package, e.g. Miri,
clippy.
This repository has lots of submodules and subtrees and various
different projects are carved out of pieces of it. It seems like
`[workspace.dependencies]` will just be more trouble than it's worth.
With the stage0 refactor the proc_macro version found in the sysroot
will no longer always match the proc_macro version that proc-macros get
compiled with by the rustc executable that uses this proc_macro. This
will cause problems as soon as the ABI of the bridge gets changed to
implement new features or change the way existing features work.
To fix this, this commit changes rustc crates to depend directly on the
local version of proc_macro which will also be used in the sysroot that
rustc will build.
