[clang] [X86_64] fix arg pass error in struct. (PR #85394)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I think the logic the code is using is that t67 is actually properly aligned: it's a type with size 8 and alignment 4, so everything is fine.  If that's not right, we should tweak the relevant logic (around line 2104).

Specifically checking whether a type crosses an 8-byte boundary seems wrong; the only relevant text I can find in the standard is just "if the size of an object is larger than eight eightbytes, or it contains unaligned fields, it has class MEMORY."

https://github.com/llvm/llvm-project/pull/85394