[llvm-cov] Drop the longest common filename prefix from summaries

Remove the longest common prefix from filenames when printing coverage
summaries. This makes them easier to compare.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280895 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed