Unable to install on OS X Sierra 

Hi Francois,

I'm having an issue building YAO on a new Macbook running OS X Sierra at the moment.

After configuring the Makefile, running `make` results in the following:

```
Undefined symbols for architecture x86_64:
  "_Y_aoSimulVersion" referenced from:
      _y0_routines in ywrap.o
ld: symbol(s) not found for architecture x86_64
```

Have you come across any similar issues?