[clang] [Clang][CodeGen][X86] don't coerce int128 into `{i64,i64}` for SysV-like ABIs (PR #135230)

[Nikita Popov via cfe-commits]

https://github.com/nikic commented:

I haven't checked the implementation, but conceptually this looks fine. Passing as i128 instead of {i64, i64} is better for optimization purposes. Rust already passes these as i128, so we know that works, and change will improve x-lang LTO. (Clang also passes as i128 already, but only for ones that are known to be passed in memory -- go figure.)

https://github.com/llvm/llvm-project/pull/135230