The majority of the code is only used by either rustbuild or
rustc_llvm's build script. Rust_build is compiled once for rustbuild and
once for every stage. This means that the majority of the code in this
crate is needlessly compiled multiple times. By moving only the code
actually used by the respective crates to rustbuild and rustc_llvm's
build script, this needless duplicate compilation is avoided.
If you have a file in the repository root with the same name as a file
somewhere within a directory, the latter currently won't get formatted.
I have experienced this multiple times and not understood what was
happening; I finally figured out the problem today. This commit fixes
the problem.
The performance difference is negligible, but it makes me feel better.
Note that this does not remove some clones in `config`, because it would
require changing the logic around (and performance doesn't matter
for bootstrap).
This replaces cargo-fmt with rustfmt with --skip-children which should
allow us to format code without running into rust-lang/rustfmt#3930.
This also bumps up the version of rustfmt used to a more recent one.
