[clang] [clang-format] Fix repeated backslash insertion in macro line comments (PR #164300)

[Ruoyu Zhong via cfe-commits]

ZhongRuoyu wrote:

> You may also want to update the commit message, because line comments **can** be continued with `\`. https://godbolt.org/z/GP8YnoTqb

Thanks -- didn't think about that! I updated the PR description as well.


https://github.com/llvm/llvm-project/pull/164300