[llvm] [Support] Fix color handling in formatted_raw_ostream (PR #86700)

[Andrew Ng via llvm-commits]

nga888 wrote:

> Nice, I like how elegant this is. Thanks for fixing this! LGTM.

Thanks for the fast review. I just spotted a minor issue with one of the assertions which was in the "wrong" place which I've now updated.

https://github.com/llvm/llvm-project/pull/86700