rustc: Stabilize the #![windows_subsystem] attribute

This commit stabilizes the `#![windows_subsystem]` attribute which is a
conservative exposure of the `/SUBSYSTEM` linker flag on Widnows platforms. This
is useful for creating applications as well as console programs.

Closes #37499

src/doc/unstable-book/src/SUMMARY.md

@@ -209,5 +209,4 @@
 - [windows_handle](windows-handle.md)
 - [windows_net](windows-net.md)
 - [windows_stdio](windows-stdio.md)
-- [windows_subsystem](windows-subsystem.md)
 - [zero_one](zero-one.md)

src/libsyntax/feature_gate.rs

@@ -292,9 +292,6 @@ declare_features! (
     // Allows attributes on lifetime/type formal parameters in generics (RFC 1327)
     (active, generic_param_attrs, "1.11.0", Some(34761)),
 
-    // The #![windows_subsystem] attribute
-    (active, windows_subsystem, "1.14.0", Some(37499)),
-
     // Allows #[link(..., cfg(..))]
     (active, link_cfg, "1.14.0", Some(37406)),
 
@@ -408,7 +405,8 @@ declare_features! (
     (accepted, static_recursion, "1.17.0", Some(29719)),
     // pub(restricted) visibilities (RFC 1422)
     (accepted, pub_restricted, "1.17.0", Some(32409)),
-
+    // The #![windows_subsystem] attribute
+    (accepted, windows_subsystem, "1.18.0", Some(37499)),
 );
 // If you change this, please modify src/doc/unstable-book as well. You must
 // move that documentation into the relevant place in the other docs, and
@@ -768,11 +766,7 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                         "unboxed_closures are still evolving",
                                         cfg_fn!(unboxed_closures))),
 
-    ("windows_subsystem", Whitelisted, Gated(Stability::Unstable,
-                                             "windows_subsystem",
-                                             "the windows subsystem attribute \
-                                              is currently unstable",
-                                             cfg_fn!(windows_subsystem))),
+    ("windows_subsystem", Whitelisted, Ungated),
 
     ("proc_macro_attribute", Normal, Gated(Stability::Unstable,
                                            "proc_macro",

src/test/compile-fail/windows-subsystem-invalid.rs

@@ -10,7 +10,6 @@
 
 // error-pattern: invalid windows subsystem `wrong`, only `windows` and `console` are allowed
 
-#![feature(windows_subsystem)]
 #![windows_subsystem = "wrong"]
 
 fn main() {}

src/test/run-make/windows-subsystem/console.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(windows_subsystem)]
 #![windows_subsystem = "console"]
 
 fn main() {}

src/test/run-make/windows-subsystem/windows.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(windows_subsystem)]
 #![windows_subsystem = "windows"]
 
 fn main() {}