Cannot pass LLC arguments through clang

Passing argument to `LLC` through `clang` does not work. E.g.:

```
patmos-clang -O2 hello.c -mllvm -mpatmos-max-subfunction-size=64
```

This should pass the `-mpatmos-max-subfunction-size=64` flag to `LLC`. However, the resulting executable does not limit the subfunction size and the flag is not passed to `LLC` as seen when using the `clang -v` flag.