[llvm] [Support] Accept -no-<name> to negate cl::opt<bool> (PR #224978)

[Nikita Popov via llvm-commits]

nikic wrote:

I'm not really convinced by this change. Maybe I'm just too used to things, but I like the current syntax, and wouldn't want it to go away.

If we really want to align cl::opt with other CLI option parsing libraries, the first thing to do would probably be to stop supporting `-foo` and require `--foo` instead -- I kinda hope that's not the plan!

https://github.com/llvm/llvm-project/pull/224978