c2hs seems to have issue with C11 _Noreturn function specifier.

Noticed this on alpine linux 3.3.1 when compiling the ncurses package.

The error log:

```
Configuring ncurses-0.2.15...
Building ncurses-0.2.15...
Preprocessing library ncurses-0.2.15...
c2hs: C header contains errors:

/usr/include/stdlib.h:44: (column 11) [ERROR] >>> Syntax error !
The symbol `void' does not fit here.
```

And that section of stdlib.h:

```
_Noreturn void abort (void);
int atexit (void (*) (void));
_Noreturn void exit (int);
_Noreturn void _Exit (int);
int at_quick_exit (void (*) (void));
_Noreturn void quick_exit (int);
```

I think it would be ok to just ignore _Noreturn in these cases correct? The function specifier doesn't really change the fact that its a function just specifies that these functions never return to their caller. I couldn't find anything in the source that seems to indicate _Noreturn is parsed at all but if I missed it let me know.