Rollup merge of rust-lang#60823 - oli-obk:used_unused_no_mangle, r=michaelwoerister

Fix incremental compilation of cdylib emitting spurious unused_attributes lint

fixes rust-lang#60050

Author: Centril

src/libsyntax/feature_gate.rs

@@ -998,7 +998,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     (sym::repr, Normal, template!(List: "C, packed, ..."), Ungated),
     (sym::path, Normal, template!(NameValueStr: "file"), Ungated),
     (sym::automatically_derived, Normal, template!(Word), Ungated),
-    (sym::no_mangle, Normal, template!(Word), Ungated),
+    (sym::no_mangle, Whitelisted, template!(Word), Ungated),
     (sym::no_link, Normal, template!(Word), Ungated),
     (sym::derive, Normal, template!(List: "Trait1, Trait2, ..."), Ungated),
     (

src/test/incremental/no_mangle.rs

@@ -0,0 +1,10 @@
+// revisions:rpass1 rpass2
+// compile-flags: --crate-type cdylib
+// skip-codegen
+
+#![deny(unused_attributes)]
+
+#[no_mangle]
+pub extern "C" fn rust_no_mangle() -> i32 {
+    42
+}

src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.rs

@@ -52,7 +52,7 @@
 //~^ WARN unused attribute
 #![path = "3800"] //~ WARN unused attribute
 #![automatically_derived] //~ WARN unused attribute
-#![no_mangle] //~ WARN unused attribute
+#![no_mangle]
 #![no_link] //~ WARN unused attribute
 // see issue-43106-gating-of-derive.rs
 #![should_panic] //~ WARN unused attribute

src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.stderr

@@ -1152,12 +1152,6 @@ warning: unused attribute
 LL | #![automatically_derived]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:55:1
-   |
-LL | #![no_mangle]
-   | ^^^^^^^^^^^^^
-
 warning: unused attribute
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:56:1
    |