EH: need to update the treatment of auto_flag for compliers other than gcc

For example, the `auto_flag=True` does not work for clang.
One can disable `auto_flag` and specify the compiler and linker args manually, e.g.,
```
cymod = cyper.inline(code,
                     auto_flag=False, 
                     extra_compile_args=['-fopenmp'],
                     extra_link_args=['-fopenmp=libiomp5']
                     )
```

