[libc] [llvm] [libc][NFC] Use user defined literals to build 128 and 256 bit constants. (PR #81746)

[via llvm-commits]

lntue wrote:

I'm sorry for asking a bit late, but is it easy to add `'` to divide 128-bit and 256-bit numbers into 32-bit or 64-bit chunks?

https://github.com/llvm/llvm-project/pull/81746