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

[Phoebe Wang via llvm-commits]

phoebewang wrote:

I see some problems here:

- The tile says it's for windows but description says for both. So the title is incorrect?
- I'd expect more tests affected by this change, e.g., https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/X86/fp128-cast.ll#L1059 should store into memory and pass to __gttf2, right?
- ABI change needs to be documented in ReleaseNote

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