Rollup merge of rust-lang#40909 - nagisa:fix-vec-placement, r=alexcrichton

Allow using Vec::<T>::place_back for T: !Clone

The place_back was likely put into block with `T: Clone` bound by mistake.

Author: Ariel Ben-Yehuda

src/libcollections/vec.rs

@@ -973,6 +973,29 @@ impl<T> Vec<T> {
         }
     }
 
+    /// Returns a place for insertion at the back of the `Vec`.
+    ///
+    /// Using this method with placement syntax is equivalent to [`push`](#method.push),
+    /// but may be more efficient.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(collection_placement)]
+    /// #![feature(placement_in_syntax)]
+    ///
+    /// let mut vec = vec![1, 2];
+    /// vec.place_back() <- 3;
+    /// vec.place_back() <- 4;
+    /// assert_eq!(&vec, &[1, 2, 3, 4]);
+    /// ```
+    #[unstable(feature = "collection_placement",
+               reason = "placement protocol is subject to change",
+               issue = "30172")]
+    pub fn place_back(&mut self) -> PlaceBack<T> {
+        PlaceBack { vec: self }
+    }
+
     /// Removes the last element from a vector and returns it, or [`None`] if it
     /// is empty.
     ///
@@ -1267,29 +1290,6 @@ impl<T: Clone> Vec<T> {
     pub fn extend_from_slice(&mut self, other: &[T]) {
         self.spec_extend(other.iter())
     }
-
-    /// Returns a place for insertion at the back of the `Vec`.
-    ///
-    /// Using this method with placement syntax is equivalent to [`push`](#method.push),
-    /// but may be more efficient.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(collection_placement)]
-    /// #![feature(placement_in_syntax)]
-    ///
-    /// let mut vec = vec![1, 2];
-    /// vec.place_back() <- 3;
-    /// vec.place_back() <- 4;
-    /// assert_eq!(&vec, &[1, 2, 3, 4]);
-    /// ```
-    #[unstable(feature = "collection_placement",
-               reason = "placement protocol is subject to change",
-               issue = "30172")]
-    pub fn place_back(&mut self) -> PlaceBack<T> {
-        PlaceBack { vec: self }
-    }
 }
 
 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.