[llvm] Remove dependence on <ciso646> (PR #73273)

[Jonas Devlieghere via llvm-commits]

JDevlieghere wrote:

> Both of these includes have already been dropped in https://github.com/llvm/llvm-project/commit/0060c54e0da6d1429875da2d30895faa7562b706 and https://github.com/llvm/llvm-project/commit/d8eb4ac41d881a19bea7673d753ba92e6a11f5d6.
> 
> 
> 
> So merging this PR effectively *only* added the incorrect <version> include...

Yeah I noticed when I saw the diff of the revert. 

https://github.com/llvm/llvm-project/pull/73273