fix: missing import

Author: Oneirical

src/tools/run-make-support/src/rustc.rs

@@ -1,6 +1,7 @@
 use std::env;
 use std::path::Path;
 use std::process::{Command, Output};
+use std::path::PathBuf;
 
 use crate::{handle_failed_output, tmp_dir};