[llvm] [Code Coverage] Add a tool to check test coverage of a patch (PR #71841)

[Shivam Gupta via llvm-commits]

xgupta wrote:

Actually, the above issue is because of -DLLVM_BUILD_TESTS=ON flag, using that in cmake, gives the list of all unit tests.

I have llvm unit tests patch - https://github.com/llvm/llvm-project/pull/71952
https://github.com/xgupta/llvm-project/actions/runs/7002086614/job/19045204411

I have clang unit test patch - https://github.com/llvm/llvm-project/pull/71672
https://github.com/xgupta/llvm-project/actions/runs/7002113619/job/19045279617

https://github.com/llvm/llvm-project/pull/71841