[clang] [LoongArch] Fix ABI mismatch with gcc/g++ about empty structs passing (PR #70320)

[Lu Weining via cfe-commits]

SixWeining wrote:

Hi @xen0n @xry111, what do you think about this change? If it is ok, I'd like to checrry-pick to release/17.x (hope it's not too late...).

https://github.com/llvm/llvm-project/pull/70320