llvm-cov: Try to appease a bot

llvm-cov: Try to appease a bot

The clang-hexagon elf bot was complaining that "Option 'color'
registered more than once!":

    http://lab.llvm.org:8011/builders/clang-hexagon-elf/builds/24425

I don't understand why this error is happening, and I don't see it on
any other bots or on my own machine, so I'm kind of grasping at
straws. Try using an unscoped enum and specifying a cl::init to see if
they help.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232698 91177308-0d34-0410-b5e6-96231b3b80d8