moving <limits> bits to config/cpu

[Benjamin Kosnik]

> I was thinking of something analogous to config.gcc's tm_file or xm_file.
> In configure.target we assign some variable (like "limits_headers" or
> something) a reasonable default, like
> 
>   limits_headers=$cpu_include_dir/bits/hardware_limits.h
> 
> and then possibly append/prepend other files to the list, like
> 
>   case "${target_os}" in
>     freebsd*)
>       limits_headers="$limits_headers $os_include_dir/bits/bsd_limits.h"
>   esac
> 
> Maybe we wouldn't want to put them in the "bits" subdir, since that
> directory is being searched directly, but you get my point.

Yes, I do. Thanks.

I'll wait for Gaby to post a summary of the new limits work before this 
goes much further. 

I'm still hoping that there is a way to re-use much of gcc's  
information for basic types so that this macro machinery is not as pervasive.
However, this might be as good as it gets. 

-benjamin