[d3d9] Do not assume 16-byte alignment in replaceNaN

[doitsujin]

Stack alignment is 4 bytes on 32-bit, and we cannot align variables on the stack, so this is technically broken. Use unaligned stores instead even if those are a bit slower.

[AlpyneDreams]

For what it's worth, I don't remember why I added the alignas in #3547 instead of just making it unaligned like in #3515, but I don't think there was a good reason. It already caused unfathomable anguish during the development of d8vk.

[misyltoad]

why can variables not be aligned? surely it can just add some and & off the stack ptr?

[doitsujin]

why can variables not be aligned? surely it can just add some and & off the stack ptr?

Ishi explained the issue, something with SEH requiring stack alignment to be done in a specific way but GCC doing it in a different way, so with a Windows target platform, GCC will just not align rsp at all and silently generate code that can explode at any time.