[clang] [clang][Docs] Move debug info flags into groups (PR #169942)

[J. Ryan Stinnett via cfe-commits]

jryans wrote:

Ah yes, indeed, it's NFC, perhaps should have emphasised that... We're only changing where the flags go in docs so that all the debug info bits are grouped together.

https://github.com/llvm/llvm-project/pull/169942