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_gcc/build_system/src/build.rs

@@ -1,12 +1,13 @@
-use crate::config::{Channel, ConfigInfo};
-use crate::utils::{
-    copy_file, create_dir, get_sysroot_dir, run_command, run_command_with_output_and_env, walk_dir,
-};
 use std::collections::HashMap;
 use std::ffi::OsStr;
 use std::fs;
 use std::path::Path;
 
+use crate::config::{Channel, ConfigInfo};
+use crate::utils::{
+    copy_file, create_dir, get_sysroot_dir, run_command, run_command_with_output_and_env, walk_dir,
+};
+
 #[derive(Default)]
 struct BuildArg {
     flags: Vec<String>,