AST Compare tests libpypa vs cpython

@kmod 
I have implemented a priliminary patch for the suggested check.
It already shows some issues. I will check them out and fix them.
I have made it now conditionally.

```
COMMON_LDFLAGS += `pkg-config tinfo && pkg-config tinfo --libs || echo ""`
```

This will now cause it to be only added if pkg-config can actually find it :-)