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/test.rs

@@ -1,3 +1,10 @@
+use std::collections::HashMap;
+use std::ffi::OsStr;
+use std::fs::{remove_dir_all, File};
+use std::io::{BufRead, BufReader};
+use std::path::{Path, PathBuf};
+use std::str::FromStr;
+
 use crate::build;
 use crate::config::{Channel, ConfigInfo};
 use crate::utils::{
@@ -6,13 +13,6 @@ use crate::utils::{
     split_args, walk_dir,
 };
 
-use std::collections::HashMap;
-use std::ffi::OsStr;
-use std::fs::{remove_dir_all, File};
-use std::io::{BufRead, BufReader};
-use std::path::{Path, PathBuf};
-use std::str::FromStr;
-
 type Env = HashMap<String, String>;
 type Runner = fn(&Env, &TestArg) -> Result<(), String>;
 type Runners = HashMap<&'static str, (&'static str, Runner)>;