This was broken since the crate's location relative to the target directory had changed.
cargo fmt
Apply the same formatting rules to both `libm` and `compiler-builtins`.
Update paths and submodules to fix `libm-test` and `util` building so we will be able to add them to the workspace.
Distribute everything from `libm/` to better locations in the repo. `libm/libm/*` has not moved yet to avoid Git seeing the move as an edit to `Cargo.toml`. Files that remain to be merged somehow are in `etc/libm`.
