RFC: adding knowledge of the int_fastN_t types to the compiler

[FX Coudert]

> it's just targets that might have them but haven't
> had the relevant information recorded in GCC that I think should  
> not have
> the types defined by default in GCC.  (How this relates to Fortran  
> is up
> to the Fortran maintainers.)

Fortran requires that a negative value be returned if the  
"int_fastN_t type isn't defined in the companion C compiler" (quoting  
from memory). Thus, of the three cases:

   1. on targets that do have int_fastN_t types defined, we register  
the information in the compiler (for Fortran, but maybe other uses)  
but don't override stdint.h
   2. on targets that don't have int_fastN_t types, we provide a  
stdint.h and give the corresponding values in Fortran
   3. on targets that have int_fastN_t types but the compiler wasn't  
updated to know, we either provide our own defaults in Fortran and  
hope they match; a carefully crafted testcase in the testsuite might  
help checking that and adding information about these targets when we  
see the testcase FAILing.

FX

-- 
François-Xavier Coudert
http://www.homepages.ucl.ac.uk/~uccafco/