This is in our amber arm64 chroot:
# dpkg-buildflags --get CFLAGS
while this is on Debian buster
# dpkg-buildflags --get CFLAGS -g -O2 -fdebug-prefix-map=/DATA/pbuilder/base-buster.cow=. -fstack-protector-strong -Wformat -Werror=format-security
both are dpkg-dev is 1.19.7.
The reason is the lack of a /usr/share/perl5/Dpkg/Vendor/PureOS.pm (which i added to our chroot to hack around this).
This currently breaks the webkit builds but should cause problems for lots of other packages (and is way less strict security wise)