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

[Jeremy Morse via cfe-commits]

https://github.com/jmorse approved this pull request.

/me squints -- so because this is only changing the grouping of options and how they're presented when displayed, this is essentially NFC as far as the input/output of the compilation process goes? Assuming I've got that right, LGTM.

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