win64 generates SSE instructions even when they are disabled with -sse

[AndrewScull]

Following the advice of #1364, I tried to avoid using SSE instructions by disabling MMX and SSE, and enabling soft-float with the features field of my tagert "features": "-mmx,-sse,+soft-float". However, when using an extern "win64" function for my UEFI entry point, movaps instructions are still generated to save and restore the xmm6-15 registers.

I have put together a minimal example to demonstate the problem.

[AndrewScull]

Don't think this was the right repo, have moved to rust-lang/rust#36653.