syntax: use box instead of Box::new in ptr::P.

src/libsyntax/lib.rs

@@ -12,6 +12,7 @@
 #![deny(unused_lifetimes)]
 
 #![feature(bind_by_move_pattern_guards)]
+#![feature(box_syntax)]
 #![feature(const_fn)]
 #![feature(const_transmute)]
 #![feature(crate_visibility_modifier)]

src/libsyntax/ptr.rs

@@ -45,7 +45,7 @@ pub struct P<T: ?Sized> {
 /// Construct a `P<T>` from a `T` value.
 pub fn P<T: 'static>(value: T) -> P<T> {
     P {
-        ptr: Box::new(value)
+        ptr: box value
     }
 }