[clang] [clang] Enable descriptions for --print-supported-extensions (PR #66715)

[David Spickett via cfe-commits]

DavidSpickett wrote:

If you are doing more contributions you can get commit access by doing https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access. Though with the switch to Github it's super easy to ask the reviewer to click the merge button, so it's not required.

https://github.com/llvm/llvm-project/pull/66715