Merge branch 'issue-2848' of github.com:chansuke/rustup into issue-2848

Author: chansuke

Diff for: src/env_var.rs

@@ -46,14 +46,10 @@ fn append_path<E: ProcessEnvs>(name: &str, value: Vec<PathBuf>, cmd: &mut E) {
 
 pub(crate) fn prepend_path<E: ProcessEnvs>(name: &str, prepend: Vec<PathBuf>, cmd: &mut E) {
     let old_value = process().var_os(name);
-    let parts = if let Some(ref v) = old_value {
-        let mut tail = env::split_paths(v).collect::<VecDeque<_>>();
-        for path in prepend.into_iter().rev() {
-            if !tail.contains(&path) {
-                tail.push_front(path);
-            }
-        }
-        tail
+    let parts: Vec<PathBuf>;
+    if let Some(ref v) = old_value {
+        let old_paths: Vec<PathBuf> = env::split_paths(v).collect::<Vec<_>>();
+        parts = concat_uniq_paths(value, old_paths);
     } else {
         prepend.into()
     };