Stabilise attributes on statements.

Note that attributes on expressions are still unstable and are behind the `stmt_expr_attributes` flag.

cc [Tracking issue](https://github.com/rust-lang/rust/issues/15701)

src/test/compile-fail/mir-dataflow/def-inits-1.rs

@@ -11,7 +11,6 @@
 // General test of maybe_uninits state computed by MIR dataflow.
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 
 use std::intrinsics::rustc_peek;
 use std::mem::{drop, replace};

src/test/compile-fail/mir-dataflow/inits-1.rs

@@ -11,7 +11,6 @@
 // General test of maybe_inits state computed by MIR dataflow.
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 
 use std::intrinsics::rustc_peek;
 use std::mem::{drop, replace};

src/test/compile-fail/mir-dataflow/uninits-1.rs

@@ -11,7 +11,6 @@
 // General test of maybe_uninits state computed by MIR dataflow.
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 
 use std::intrinsics::rustc_peek;
 use std::mem::{drop, replace};

src/test/compile-fail/mir-dataflow/uninits-2.rs

@@ -11,7 +11,6 @@
 // General test of maybe_uninits state computed by MIR dataflow.
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 
 use std::intrinsics::rustc_peek;
 use std::mem::{drop, replace};

src/test/compile-fail/stmt_expr_attrs_no_feature.rs

@@ -21,15 +21,15 @@ fn main() {
     #[attr]
     fn a() {}
 
-    #[attr] //~ ERROR 15701
+    #[attr]
     {
 
     }
 
-    #[attr] //~ ERROR 15701
+    #[attr]
     5;
 
-    #[attr] //~ ERROR 15701
+    #[attr]
     stmt_mac!();
 }
 
@@ -43,7 +43,7 @@ fn c() {
 
 #[cfg(not(unset))]
 fn j() {
-    #[attr] //~ ERROR 15701
+    #[attr]
     5;
 }
 
@@ -55,7 +55,7 @@ fn d() {
 
 #[cfg_attr(not(unset), cfg(not(unset)))]
 fn i() {
-    #[attr] //~ ERROR 15701
+    #[attr]
     8;
 }
 
@@ -64,7 +64,7 @@ fn i() {
 macro_rules! item_mac {
     ($e:ident) => {
         fn $e() {
-            #[attr] //~ ERROR 15701
+            #[attr]
             42;
 
             #[cfg(unset)]
@@ -75,7 +75,7 @@ macro_rules! item_mac {
 
             #[cfg(not(unset))]
             fn k() {
-                #[attr] //~ ERROR 15701
+                #[attr]
                 5;
             }
 
@@ -87,7 +87,7 @@ macro_rules! item_mac {
 
             #[cfg_attr(not(unset), cfg(not(unset)))]
             fn h() {
-                #[attr] //~ ERROR 15701
+                #[attr]
                 8;
             }
 

src/test/run-pass/const-negation.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(stmt_expr_attributes)]
-
 #[deny(const_err)]
 
 fn main() {

src/test/run-pass/enum-discrim-autosizing.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(stmt_expr_attributes)]
-
 use std::mem::size_of;
 
 enum Ei8 {

src/test/run-pass/issue-8460.rs

@@ -11,7 +11,7 @@
 // ignore-emscripten no threads support
 // ignore-pretty : (#23623) problems when  ending with // comments
 
-#![feature(rustc_attrs, stmt_expr_attributes, zero_one)]
+#![feature(rustc_attrs, zero_one)]
 
 use std::num::Zero;
 use std::thread;