Don't build rustc_middle for x.py build src/tools/rustfmt #82206
Description
Rustfmt only depends on the parser, not type checking, and building rustc_middle greatly increases the time it takes to build.
$ x.py build --stage 0 src/tools/rustfmt Updating only changed submodules Submodules updated in 0.01 seconds Compiling bootstrap v0.0.0 (/home/joshua/rustc2/src/bootstrap) Finished dev [unoptimized + debuginfo] target(s) in 12.04s Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu) Finished release [optimized] target(s) in 0.15s Copying stage0 std from stage0 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu / x86_64-unknown-linux-gnu) Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu) Compiling rustc_middle v0.0.0 (/home/joshua/rustc2/compiler/rustc_middle) Building [=====================> ] 195/217: rustc_middle