clang-format: Improve free-standing macro detection.

Before:
  SOME_WEIRD_LOG_MACRO
  << "Something long enough to cause a line break";

After:
  SOME_WEIRD_LOG_MACRO
      << "Something long enough to cause a line break";

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@221338 91177308-0d34-0410-b5e6-96231b3b80d8