add PathBuf import

Author: Oneirical

tests/run-make/issue-11908/rmake.rs

@@ -13,6 +13,7 @@
 
 use run_make_support::{rustc, dynamic_lib, tmp_dir};
 use std::fs;
+use std::path::PathBuf;
 
 fn main() {
     let mut tmp_dir_other = tmp_dir();