[clang-format] don't break up #-style comment sections

Follow-up from https://github.com/llvm/llvm-project/commit/36d13d3f8adb3d1a6bae71370afa23d11a94dc78; https://reviews.llvm.org/D121451.

Restore the old behavior in situations where we use # as comments and long strings of #'s for comment sections.

Reviewed By: MyDeveloperDay

Differential Revision: https://reviews.llvm.org/D122230