By setting limit_to_features to a non empty list of features a configuration can
restrict the set of tests to run to only include tests that require a feature in
this list.
rdar://21082253
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238766 91177308-0d34-0410-b5e6-96231b3b80d8