Re-introduce kill_session::exit_status, @lenormf was right

As discussed in #2186, in the end we need the exit status for the
case where the local client exited first (the server forked to
background) then another client trigger the kill command.

src/commands.cc

@@ -446,7 +446,7 @@ void kill(const ParametersParser& parser, Context& context, const ShellContext&)
     while (not client_manager.empty())
         client_manager.remove_client(**client_manager.begin(), true, status);
 
-    throw kill_session{};
+    throw kill_session{status};
 }
 
 const CommandDesc kill_cmd = {

src/commands.hh

@@ -6,7 +6,10 @@ namespace Kakoune
 
 void register_commands();
 
-struct kill_session {};
+struct kill_session
+{
+    int exit_status;
+};
 
 }
 

src/main.cc

@@ -760,7 +760,10 @@ int run_server(StringView session, StringView server_init,
             }
         }
     }
-    catch (const kill_session&) {}
+    catch (const kill_session& kill)
+    {
+        local_client_exit = kill.exit_status;
+    }
 
     {
         Context empty_context{Context::EmptyContextFlag{}};