[WIP PATCH]: Add __builtin_va_arg_bitint, __builtin_bitint_unpack and __builtin_bitint_pack builtins

[Joseph Myers]

On Mon, 6 Jul 2026, Martin Uecker wrote:

> Do we need the full generality, i.e.  support for LE, BE and
> any limb type or could we simply fix this to whatever corresponds
> to the ABI?  Maybe I am missing something obvious.

I'd expect glibc to use such a feature together with the __mpn_* bits of 
GMP that are already used for some purposes in printf / strtod.  That 
means using LE together with the mp_libm_t type used in glibc, which need 
not match the _BitInt endianness or libm size (thus, a feature restricted 
to following the _BitInt ABI more closely would be less convenient to use 
in glibc).

-- 
Joseph S. Myers
josmyers@redhat.com