Detect float type for :auto type in grovel

[Song Wei]

made a implement:
https://github.com/leosongwei/cffi/compare/master...leosongwei:dev

gonna make a pull request after adding test

On 2021/3/23 下午10:15, Song Wei wrote:
> Just checked the
> https://github.com/cffi/cffi/blob/master/grovel/common.h , there is a
> SLOT_SIGNED_P macro, which looks very interesting.
> 
> I'm wondering is it a good idea to use similar trick to detect float and
> double for the auto type?
>