Builds the uutils multicall binary containing all utils (except stdbuf)
by default. To only build a subset
`cargo --no-default-features --features <utils>`
can be used.
Whats missing is building the standalone binaries and a mechanism to
automatically disable the build of unix only utils on windows.
This patch begins the work of modernizing uutils to work with 1.0-ish
Rust. In particular, it
1. Updates to the latest submodules.
2. Convert mkmain.rs, mkuutils.rs, and src/uutils/uutils.rs
to new slice syntax and use of new io, fs, and path APIs.
3. Convert src/common/util.rs to new io, fs, and path APIs.
4. Convert fmt to use new APIs.