Hmm, looks like bscript is starting to bitrot.
```
    # TODO: add OPTIONAL_HEADERS, OPTIONAL_INTRINSICS and
    # OPTIONAL_GCC_ATTRIBUTES (see setup.py and gh-3766).  These are
    # performance optimizations for GCC.
```
It's already missing stuff. Adding the new stuff to `setup_common.py` would be a place to start, but looks like more needs to be done. Hmm, @cournape Why is `bscript` not `bscript.py`?

I'm beginning to think bento isn't worth worrying about until it comes up to speed. Might be worth adding `["__thread", "__declspec(thread)"]` to `setup_common.py` though, just as a start. What would be a good name for that list?