I should add:
dpkg-buildflags manpage does not list DFLAGS as a supported flag, but
explicitly mentioned that more flags might get added in the future if
needed for more languages.
DFLAGS was added with
commit d01d1f49c9734a39fc278f4d5b75444c96491023
Author: Guillem Jover <guil...@debian.org>
Date: Fri Nov 27 01:52:28 2020 +0100
dpkg-buildflags: Add support for DFLAGS
Add default value in Debian and derivatives for the flag.
It will get either -fdebug or -frelease depending on noopt presence in
DEB_BUILD_OPTIONS, but for now nothing else, as it seems common for D
project to use CPPFLAGS and CFLAGS anyway.
Closes: #975896
