[09/nn] Add a fixed_size_mode_pod class

[Eric Botcazou]

> There's always the possibility of building GCC 4.8 with the other compiler
> and then GCC 9+ (?) with GCC 4.8.

What an user-friendly solution...

> What's the list of other compilers people routinely use?  I see various
> comments on other compilers in install.texi but those are already saying
> those cannot be used to build GCC but you need to build an older GCC first
> (like xlc or the HP compiler).

I read the opposite for XLC:

"GCC can bootstrap with recent versions of IBM XLC, but bootstrapping with an 
earlier release of GCC is recommended."

I think that the major supported compilers are IBM, Sun/Oracle and LLVM.

-- 
Eric Botcazou