autoconf macro to get integer sizes in bits

[johnwohlbier]

I'm wondering about the existence of a macro that sets integer sizes in  
bits. We'd like to define variables to AC_SUBST into header.in files to set  
int32_t, int64_t, etc. based on the results of the desired macro.

I'm aware of the existence of AC_CHECK_SIZEOF that returns integer sizes in  
bytes. If we have to write the macro ourselves we'd probably use these. I'm  
just wondering if someone has already done the work to get the bit sizes  
back. One macro call that sets results for long, long long, etc. would be  
ideal.

Thanks.
jgw