Update tests/test_stl.cpp

Author: henryiii

tests/test_stl.cpp

@@ -119,7 +119,8 @@ class ReferenceSensitiveOptional {
 public:
     using value_type = T;
 
-    ReferenceSensitiveOptional() = default;
+    // NOLINTNEXTLINE(modernize-use-equals-default): breaks GCC 4.8
+    ReferenceSensitiveOptional() {};
     // NOLINTNEXTLINE(google-explicit-constructor)
     ReferenceSensitiveOptional(const T& value) : storage{value} {}
     // NOLINTNEXTLINE(google-explicit-constructor)