[llvm] [llvm-cov] Support LCOV exclusion markers (PR #220767)

[Yaxun Liu via llvm-commits]

yxsamliu wrote:

@evodius96 I posted a brief [RFC](https://discourse.llvm.org/t/rfc-source-coverage-exclusion-markers-in-llvm-cov/91977) describing the feature and linking this PR. Thanks for suggesting the option and LLVM marker names.

https://github.com/llvm/llvm-project/pull/220767