[llvm] [windows] Always pass libcall fp128 arguments indirectly (PR #128848)

[Reid Kleckner via llvm-commits]

rnk wrote:

I went looking at `X86TargetLowering::LowerWin64_i128OP`. I think that logic exists to manually implement the calling convention logic that you've implemented here, and perhaps we just don't need this logic anymore. I can't think of any specific concerns.

https://github.com/llvm/llvm-project/pull/128848