Update tests for extern block linting

Author: Mark-Simulacrum

compiler/rustc_error_codes/src/error_codes/E0044.md

@@ -3,13 +3,13 @@ You cannot use type or const parameters on foreign items.
 Example of erroneous code:
 
 ```compile_fail,E0044
-extern { fn some_func<T>(x: T); }
+extern "C" { fn some_func<T>(x: T); }
 ```
 
 To fix this, replace the generic parameter with the specializations that you
 need:
 
 ```
-extern { fn some_func_i32(x: i32); }
-extern { fn some_func_i64(x: i64); }
+extern "C" { fn some_func_i32(x: i32); }
+extern "C" { fn some_func_i64(x: i64); }
 ```

compiler/rustc_error_codes/src/error_codes/E0130.md

@@ -3,7 +3,7 @@ A pattern was declared as an argument in a foreign function declaration.
 Erroneous code example:
 
 ```compile_fail,E0130
-extern {
+extern "C" {
     fn foo((a, b): (u32, u32)); // error: patterns aren't allowed in foreign
                                 //        function declarations
 }
@@ -17,15 +17,15 @@ struct SomeStruct {
     b: u32,
 }
 
-extern {
+extern "C" {
     fn foo(s: SomeStruct); // ok!
 }
 ```
 
 Or:
 
 ```
-extern {
+extern "C" {
     fn foo(a: (u32, u32)); // ok!
 }
 ```

compiler/rustc_error_codes/src/error_codes/E0454.md

@@ -3,13 +3,13 @@ A link name was given with an empty name.
 Erroneous code example:
 
 ```compile_fail,E0454
-#[link(name = "")] extern {}
+#[link(name = "")] extern "C" {}
 // error: `#[link(name = "")]` given with empty name
 ```
 
 The rust compiler cannot link to an external library if you don't give it its
 name. Example:
 
 ```no_run
-#[link(name = "some_lib")] extern {} // ok!
+#[link(name = "some_lib")] extern "C" {} // ok!
 ```

compiler/rustc_error_codes/src/error_codes/E0455.md

@@ -4,15 +4,15 @@ as frameworks are specific to that operating system.
 Erroneous code example:
 
 ```ignore (should-compile_fail-but-cannot-doctest-conditionally-without-macos)
-#[link(name = "FooCoreServices", kind = "framework")] extern {}
+#[link(name = "FooCoreServices", kind = "framework")] extern "C" {}
 // OS used to compile is Linux for example
 ```
 
 To solve this error you can use conditional compilation:
 
 ```
 #[cfg_attr(target="macos", link(name = "FooCoreServices", kind = "framework"))]
-extern {}
+extern "C" {}
 ```
 
 Learn more in the [Conditional Compilation][conditional-compilation] section

compiler/rustc_error_codes/src/error_codes/E0458.md

@@ -3,7 +3,7 @@ An unknown "kind" was specified for a link attribute.
 Erroneous code example:
 
 ```compile_fail,E0458
-#[link(kind = "wonderful_unicorn")] extern {}
+#[link(kind = "wonderful_unicorn")] extern "C" {}
 // error: unknown kind: `wonderful_unicorn`
 ```
 

compiler/rustc_error_codes/src/error_codes/E0459.md

@@ -3,13 +3,13 @@ A link was used without a name parameter.
 Erroneous code example:
 
 ```compile_fail,E0459
-#[link(kind = "dylib")] extern {}
+#[link(kind = "dylib")] extern "C" {}
 // error: `#[link(...)]` specified without `name = "foo"`
 ```
 
 Please add the name parameter to allow the rust compiler to find the library
 you want. Example:
 
 ```no_run
-#[link(kind = "dylib", name = "some_lib")] extern {} // ok!
+#[link(kind = "dylib", name = "some_lib")] extern "C" {} // ok!
 ```

compiler/rustc_error_codes/src/error_codes/E0617.md

@@ -3,7 +3,7 @@ Attempted to pass an invalid type of variable into a variadic function.
 Erroneous code example:
 
 ```compile_fail,E0617
-extern {
+extern "C" {
     fn printf(c: *const i8, ...);
 }
 
@@ -21,7 +21,7 @@ to import from `std::os::raw`).
 In this case, `c_double` has the same size as `f64` so we can use it directly:
 
 ```no_run
-# extern {
+# extern "C" {
 #     fn printf(c: *const i8, ...);
 # }
 unsafe {

compiler/rustc_error_codes/src/error_codes/E0724.md

@@ -18,7 +18,7 @@ the function inside of an `extern` block.
 ```
 #![feature(ffi_returns_twice)]
 
-extern {
+extern "C" {
    #[ffi_returns_twice] // ok!
    pub fn foo();
 }

compiler/rustc_llvm/src/lib.rs

@@ -38,7 +38,7 @@ pub fn initialize_available_targets() {
         ($cfg:meta, $($method:ident),*) => { {
             #[cfg($cfg)]
             fn init() {
-                extern {
+                extern "C" {
                     $(fn $method();)*
                 }
                 unsafe {

library/core/src/sync/atomic.rs

@@ -809,7 +809,7 @@ impl AtomicBool {
     /// ```ignore (extern-declaration)
     /// # fn main() {
     /// use std::sync::atomic::AtomicBool;
-    /// extern {
+    /// extern "C" {
     ///     fn my_atomic_op(arg: *mut bool);
     /// }
     ///
@@ -2068,7 +2068,7 @@ macro_rules! atomic_int {
             /// # fn main() {
             #[doc = concat!($extra_feature, "use std::sync::atomic::", stringify!($atomic_type), ";")]
             ///
-            /// extern {
+            /// extern "C" {
             #[doc = concat!("    fn my_atomic_op(arg: *mut ", stringify!($int_type), ");")]
             /// }
             ///