NFC Add missing newline

Author: steakhal

clang/test/Analysis/Inputs/system-header-simulator-cxx-std-locks.h

@@ -14,4 +14,4 @@ template <typename T> struct lock_guard {
   lock_guard<T>(std::mutex) {}
   ~lock_guard<T>() {}
 };
-} // namespace std
+} // namespace std