Auto merge of rust-lang#87781 - est31:remove_box, r=oli-obk

Remove box syntax from compiler and tools

Removes box syntax from the compiler and tools. In rust-lang#49733, the future of box syntax is uncertain and the use in the compiler was listed as one of the reasons to keep it. Removal of box syntax [might affect the code generated](rust-lang#49646 (comment)) and slow down the compiler so I'd recommend doing a perf run on this.

Author: bors

compiler/rustc_ast/src/lib.rs

@@ -8,7 +8,6 @@
     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
     test(attr(deny(warnings)))
 )]
-#![feature(box_syntax)]
 #![feature(box_patterns)]
 #![cfg_attr(bootstrap, feature(const_fn_transmute))]
 #![feature(crate_visibility_modifier)]

compiler/rustc_ast/src/ptr.rs

@@ -37,7 +37,7 @@ pub struct P<T: ?Sized> {
 /// Construct a `P<T>` from a `T` value.
 #[allow(non_snake_case)]
 pub fn P<T: 'static>(value: T) -> P<T> {
-    P { ptr: box value }
+    P { ptr: Box::new(value) }
 }
 
 impl<T: 'static> P<T> {