LibCore: Make Process::wait_for_termination return exit code

Author: https://github.com/stasoid
Commit: 866609c682
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2377
Reviewed-by: https://github.com/ADKaster ✅

Libraries/LibCore/Process.h

@@ -79,8 +79,7 @@ public:
     ErrorOr<void> disown();
 #endif
 
-    // FIXME: Make it return an exit code.
-    ErrorOr<bool> wait_for_termination();
+    ErrorOr<int> wait_for_termination();
 
 private:
 #ifndef AK_OS_WINDOWS