Reintroduce reversed form of vespalib::string equality comparison operators
when compiling with gcc 13.
@@ -654,7 +654,7 @@ template<uint32_t StackSize>
small_string<StackSize>
operator + (const char * a, const small_string<StackSize> & b);
-#if __cplusplus < 201709L
+#if __cplusplus < 201709L || (!defined(__clang__) && __GNUC__ == 13)
template<typename T, uint32_t StackSize>
bool
operator == (const T& a, const small_string<StackSize>& b) noexcept
