Add support for clang and llvm-cov

[nijel]

It would be great if coverage would work for llvm as well out of the box. It provides quite similar interface to gcov, it just has to be executed as llvm-cov gcov, see http://llvm.org/docs/CommandGuide/llvm-cov.html

It's usage could be specified by parameter or autodected based on CC environment (use llvm-cov if CC is clang).

[stevepeak]

@nijel would love to. Do you have any open source projects showing off how llvm is used so I can review its process. Thanks!

[nijel]

I use it to build some projects on Travis CI, but meanwhile I've realized that the LLVM version there is quite old and the llvm-cov is probably not flexible enough to do what is needed.

But with recent version, all what should be needed is to run llvm-cov gcov instead of gcov. It seems to support all needed options...

[stevepeak]

@nijel perhaps other customers are having related issues, even though I have not heard of any to my knowledge. Do you have any suggestions on how to "automatically" detect when we should use llvm-cov gcov instead of gcov?

https://github.com/codecov/codecov-bash/blob/346e91cb2918fd1d84fde46c0814ae2005fee363/codecov#L484

You can already specify a custom "gcov" via -x "llvm-cov gcov"

[nijel]

The only idea is to base this on CC environment variable. That should work quite reliable for Travis CI, but not sure about other environments...

[stevepeak]

@nijel I'm not familiar with the working of llvm-cov, but would invite a pull request to review your suggestions on how to implement this. Thanks!

[nijel]

I will look into this once Travis has upgraded LLVM to more recent version which behaves better in regards to coverage.