[llvm] [llvm-cov] Add show-function-summary option in coverage report (PR #172980)

[Alan Phipps via llvm-commits]

evodius96 wrote:

In general, LGTM. Can you add a small test case to show that the option works? You may be able to extend an existing test. 

Also, just curious what use case you are aiming for to diable function coverage. Just to add more granularity to the report? Thanks!

https://github.com/llvm/llvm-project/pull/172980