llvm-cov: Print coverage summary to STDOUT.

File summaries will now be optionally outputted which will give line,
branching and call coverage info. Unfortunately, clang's current
instrumentation does not give enough information to deduce function
calls, something that gcc is able to do. Thus, no calls are always
outputted to be consistent with gcov output.

Also updated tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197606 91177308-0d34-0410-b5e6-96231b3b80d8