[clang] [llvm] [clang][CoverageMapping] Refactor when setting MC/DC True/False (PR #78202)

[Alan Phipps via cfe-commits]

evodius96 wrote:

> Could you mention the issue #77873 in the description or in the subject?

Yes, I will change this!

https://github.com/llvm/llvm-project/pull/78202