[clang] [clang] Use `cwg_index.html` from GitHub for DR status page (PR #90352)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

CI has been failing because of unrelated `Clang :: Driver/amdgpu-toolchain.c` test. I'm merging this as is.

https://github.com/llvm/llvm-project/pull/90352