[llvm-cov] Don't use colored output until we know it's supported

CodeCoverageTool::error() depends on CoverageViewOptions::Colors being
initialized. Should fix:

  http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/56

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285103 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed