Update tests for extern block linting

Author: Mark-Simulacrum

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), ");")]
             /// }
             ///

std/src/ffi/c_str.rs

@@ -86,7 +86,7 @@ use crate::sys;
 /// use std::ffi::CString;
 /// use std::os::raw::c_char;
 ///
-/// extern {
+/// extern "C" {
 ///     fn my_printer(s: *const c_char);
 /// }
 ///
@@ -144,7 +144,7 @@ pub struct CString {
 /// use std::ffi::CStr;
 /// use std::os::raw::c_char;
 ///
-/// extern { fn my_string() -> *const c_char; }
+/// extern "C" { fn my_string() -> *const c_char; }
 ///
 /// unsafe {
 ///     let slice = CStr::from_ptr(my_string());
@@ -159,7 +159,7 @@ pub struct CString {
 /// use std::os::raw::c_char;
 ///
 /// fn work(data: &CStr) {
-///     extern { fn work_with(data: *const c_char); }
+///     extern "C" { fn work_with(data: *const c_char); }
 ///
 ///     unsafe { work_with(data.as_ptr()) }
 /// }
@@ -174,7 +174,7 @@ pub struct CString {
 /// use std::ffi::CStr;
 /// use std::os::raw::c_char;
 ///
-/// extern { fn my_string() -> *const c_char; }
+/// extern "C" { fn my_string() -> *const c_char; }
 ///
 /// fn my_string_safe() -> String {
 ///     unsafe {
@@ -359,7 +359,7 @@ impl CString {
     /// use std::ffi::CString;
     /// use std::os::raw::c_char;
     ///
-    /// extern { fn puts(s: *const c_char); }
+    /// extern "C" { fn puts(s: *const c_char); }
     ///
     /// let to_print = CString::new("Hello!").expect("CString::new failed");
     /// unsafe {
@@ -465,7 +465,7 @@ impl CString {
     /// use std::ffi::CString;
     /// use std::os::raw::c_char;
     ///
-    /// extern {
+    /// extern "C" {
     ///     fn some_extern_function(s: *mut c_char);
     /// }
     ///
@@ -1147,7 +1147,7 @@ impl CStr {
     /// use std::ffi::CStr;
     /// use std::os::raw::c_char;
     ///
-    /// extern {
+    /// extern "C" {
     ///     fn my_string() -> *const c_char;
     /// }
     ///