MFC r337964, r338232: dtc(1) updates

MFC r337964, r338232: dtc(1) updates

r337964:
dtc(1): Update to 97d2d5715eeb45108cc60367fdf6bd5b2046b050

Notable fixes:
- Overlays may now be generated properly without -@
- /__local_fixups__ were not including unit address in their structure
- The error reporting a magic token was misleading, reporting
  "Bad magic token in header.  Got d00dfeed expected 0xd00dfeed"
  if the token was missing. This has been split out into a separate message.

r338232:
dtc(1): Update to 0892ec7; HACKING and implicit header fixes

Fixes courtesy of arichardson and jmg:
- HACKING was pointing to the wrong place
- Added headers were being relied on implicitly, but libstdc++ did not
  comply with the unspoken wishes of dtc.