Add basic CTF support and a CTF-powered pretty-printer to ddb.
The db_ctf.* files expose a basic interface for fetching type
data for ELF symbols, interacting with the CTF string table,
and translating type identifiers to type data.
The db_pprint.c file uses those interfaces to implement
a pretty-printer for all kernel ELF symbols.
The pretty-printer works with symbol names and arbitrary addresses:
pprint struct thread 0xffffffff8194ad90
Pretty-printing currently only works after the root filesystem
gets mounted because the CTF info is not available during
early boot.
Differential Revision: https://reviews.freebsd.org/D37899
Approved by: markj (mentor)
c21bc6f3c2