[llvm-cov] Add a debug mode for source range highlighting (in html)

llvm-cov's `-dump' option now emits information which helps debug source
range highlighting in html mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276924 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed