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

[Shivam Gupta via llvm-commits]

xgupta wrote:

Hi,

I have run it for patch - https://github.com/llvm/llvm-project/pull/71894 which is for the clang binary and .c test cases.

There are two lines not covered by any test case -
https://github.com/xgupta/llvm-project/actions/runs/6966481292/job/18956707023#step:5:3733

Here I have to change the way to run the tool -
From 
python3 git-check-coverage.py -b build bin/opt llvm/test

To 
python3 git-check-coverage.py -b build bin/clang clang/test

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