Fix comment indentation before labels.

Before:
switch (x) {
  // if 1, do f()
case 1:
  f();
}

After:
switch (x) {
// if 1, do f()
case 1:
  f();
}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176953 91177308-0d34-0410-b5e6-96231b3b80d8