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

[Trevor Gross via llvm-commits]

tgross35 wrote:

@rnk in https://github.com/llvm/llvm-project/pull/115052#issuecomment-2458268283 you mentioned that changes in `X86ISelLowering` may be needed - any idea what these would look like? The test changes here seem fine but I'm also not sure what failure modes I should be looking for.

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