I started with that approach, but it goes against the codestyle since it would need a seperate header (noreturn is also used elsewhere) so I reverted.. 
The header can be 'light' though, i.e.

```
#ifndef _MSC_VER
    #define NORETURN
#else
    #define NORETURN __attribute__((noreturn))
#endif
```

What filename do you prefer?

Another option would be to define it in mpconfig.h, and then *always* include mpconfig.h first in the c files, before nlr.h? But then pretty much all source files should change. On the other hand it's maybe not bad to always have the config first?