rustc: Stabilize #[wasm_import_module]

This commit stabilizes the `#[wasm_import_module]` attribute. Tracked by #52090
this issue can be attached to foreign modules (`extern { ... }` blocks) and is
used to configured the module name that the imports are listed with. The
WebAssembly specification indicates two utf-8 names are associated with all
imported items, one for the module the item comes from and one for the item
itself. The item itself is configurable in Rust via its identifier or
`#[link_name = "..."]`, but the module name was previously not configurable and
defaulted to `"env"`. This commit ensures that this is also configurable.

Closes #52090

Author: alexcrichton

src/libsyntax/feature_gate.rs

@@ -420,9 +420,6 @@ declare_features! (
     // The #[wasm_custom_section] attribute
     (active, wasm_custom_section, "1.26.0", Some(51088), None),
 
-    // The #![wasm_import_module] attribute
-    (active, wasm_import_module, "1.26.0", Some(52090), None),
-
     // Allows keywords to be escaped for use as identifiers
     (active, raw_identifiers, "1.26.0", Some(48589), None),
 
@@ -626,6 +623,8 @@ declare_features! (
     (accepted, global_allocator, "1.28.0", Some(27389), None),
     // Allows `#[repr(transparent)]` attribute on newtype structs
     (accepted, repr_transparent, "1.28.0", Some(43036), None),
+    // The #![wasm_import_module] attribute
+    (accepted, wasm_import_module, "1.29.0", Some(52090), None),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must
@@ -980,10 +979,7 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
         "the `#[no_debug]` attribute was an experimental feature that has been \
          deprecated due to lack of demand",
         cfg_fn!(no_debug))),
-    ("wasm_import_module", Normal, Gated(Stability::Unstable,
-                                 "wasm_import_module",
-                                 "experimental attribute",
-                                 cfg_fn!(wasm_import_module))),
+    ("wasm_import_module", Normal, Ungated),
     ("omit_gdb_pretty_printer_section", Whitelisted, Gated(Stability::Unstable,
                                                        "omit_gdb_pretty_printer_section",
                                                        "the `#[omit_gdb_pretty_printer_section]` \

src/test/run-make/wasm-import-module/bar.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_type = "cdylib"]
-#![feature(wasm_import_module)]
 #![deny(warnings)]
 
 extern crate foo;

src/test/run-make/wasm-import-module/foo.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_type = "rlib"]
-#![feature(wasm_import_module)]
 #![deny(warnings)]
 
 #[wasm_import_module = "./dep"]

src/test/ui/feature-gate-wasm_import_module.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(wasm_import_module)]
+
 
 #[wasm_import_module] //~ ERROR: must be of the form
 extern {}