Reformat use declarations.

The previous commit updated `rustfmt.toml` appropriately. This commit is
the outcome of running `x fmt --all` with the new formatting options.

compiler/rustc_codegen_cranelift/build_system/main.rs

@@ -2,9 +2,8 @@
 #![warn(unused_lifetimes)]
 #![warn(unreachable_pub)]
 
-use std::env;
 use std::path::PathBuf;
-use std::process;
+use std::{env, process};
 
 use self::utils::Compiler;