These tests assume intel-80 bit floats, as noted in their comments. Rather than having each target discover the incompatibility and disable them ad-hoc, mark them as requiring x86.
I like the idea of a feature check, rather than a specific architecture check--that is clearly the right thing to do.
On the other hand, I would like to mark the test as unsupported and not run in that case, rather than running it, saying it passed, but not actually testing anything. That better reflects the state of the implementation. Unfortunately, I don't think that can be done with macro checks. So my preference would be this patch over D31573, but I would also find D31573 acceptable if it came to that.
Finally, 80-bit doubles are a bit of a historical artifact these days. Only x86 and m68k have them (and not even all m68Ks either). So I don't think it matters that much.