[llvm] X86: don't fallback to X86-32 calling convention in 64bit mode. (PR #225820)

[James Y Knight via llvm-commits]

jyknight wrote:

Adjusting `X86_64ABIInfo::getIndirectReturnResult` may make Clang never emit this LLVM IR, but we should never emit an x87 stack use for any calls on float/double, ever, even on IR clang never emits...it's just broken behavior. So I'd like to submit this, even so.

I'm not clear if your last message means you're now OK with this change or if you want to do more investigation first. Please LMK, thanks!

https://github.com/llvm/llvm-project/pull/225820