Build failed using gcc-4.9.2

Build is failed on Ubuntu 15.04 with gcc-4.9.2:

```
/home/egavrin/dev/cj/jerryscript/jerry-core/mem/mem-heap.cpp:74:20: error: anonymous scoped enum is not allowed
 typedef enum class : uint8_t
                    ^
compilation terminated due to -Wfatal-errors.
```
