simd-arch.h depends on hedley.h

The comments at the beginning of simd-arch.h say:

```
* This was originally created for SIMDe
 * <https://github.com/simd-everywhere/simde> (hence the prefix), but this
 * header has no dependencies and may be used anywhere.  
```

...and yet, simd-arch.h includes hedley.h.
Is this intentional? 