llvm-cov: Added -f option for function summaries.

Similar to the file summaries, the function summaries output line,
branching and call statistics. The file summaries have been moved
outside the initial loop so that all of the function summaries can be
outputted before file summaries.

Also updated test cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197633 91177308-0d34-0410-b5e6-96231b3b80d8