[x86] avoid adc/sbb assert when both sides of add are zexted (PR32316)

As noted in the comment, we might want to account for this case,
but I didn't look at what that would mean for the asm. 

I'm also not sure why this only reproduces with avx512, but I'm 
putting a conservative fix in for now to avoid the crash. 

Also, if both sides of an add are zexted, shouldn't we shrink that add?

https://bugs.llvm.org/show_bug.cgi?id=32316

llvm-svn: 298107