clang-format: Extends formatted ranges to subsequent lines comments.

Before:
  int aaaa;     // This line is formatted.
                // The comment continues ..
                // .. here.

Before:
  int aaaa; // This line is formatted.
            // The comment continues ..
            // .. here.

This fixes llvm.org/PR17914.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195954 91177308-0d34-0410-b5e6-96231b3b80d8