[llvm] [X86] Enable unaligned loads on x86 using cmpxchg (PR #142645)

[via llvm-commits]

AZero13 wrote:

the actual condition is that the value must fit in a single cache line
which I think means no straddling 64-byte boundaries
(aligned values always fit in a single cache line)

How can I ensure this? 

https://github.com/llvm/llvm-project/pull/142645