At least for !10716, we can use SSE instructions in the optimized resampler (just SSE1, no SSE2+ instructions needed at the moment) when available, and we can still manage without them, thus the idea of defaulting to -msse, but not forcing it. If we want to require SSE2 on x86 going forward then sure, no reason to do it this way.
If we are going to require SSE, then there are other places where we could take advantage of it, and SSE2 would be more useful, without making much difference in terms of supported hardware. If we are not going to require it, then the right way would be `#pragma GCC target` and a runtime check. But it's probably not worth the trouble nowadays.
WRT the x86-64 architecture check, is it logically incorrect or does it just feel awkward / messy?
It's logically incorrect, building 64-bit code doesn't imply anything about the runtime CPU. For instance I routinely build ARM64 PE files on my (amd64) box, that doesn't imply that my CPU can run ARM64 code. -- https://gitlab.winehq.org/wine/wine/-/merge_requests/10953#note_140775