[clang] [clang] Add sections to C++ DR status page (PR #165749)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> My only real hesitation is that the table is currently sized to match the tables in cxx_status.html and c_status.html, so we'd lose a little inter-page consistency, but I think that's probably fine.

I don't think there is a lot of users out there to appreciate the consistency between C++ DR status page and C++ status page, so I agree that this is a minor concern.

https://github.com/llvm/llvm-project/pull/165749