[llvm-opt-report] Don't leave space for opts that never happen

[llvm-opt-report] Don't leave space for opts that never happen

Because screen space is precious, if an optimization (vectorization, for
example) never happens, don't leave empty space for the associated markers on
every line of the output. This makes the output much more compact, and allows
for the later inclusion of markers for more (although perhaps rare)
optimizations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@283626 91177308-0d34-0410-b5e6-96231b3b80d8