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

[Shivam Gupta via llvm-commits]

xgupta wrote:

I have tested it on an llc binary and .mir test case patch - https://github.com/llvm/llvm-project/pull/72388.

It works and shows three lines are not covered for two source files on standard output and there is a log file as artifect which has detailed log of coverage data - https://github.com/xgupta/llvm-project/suites/18461817041/artifacts/1070751301.

https://github.com/xgupta/llvm-project/actions/runs/6977269225/job/18986837631#step:5:2602

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