re: dpkg-buildpackage now sets DEB_BUILD_HOST etc for you?
Now, you can build packages without using dpkg-buildpackage by calling
rules directly, and in that case the rules file would need to call
dpkg-architecture, but someone would have to convince me that that was
an interface worth supporting for non-native builds
The big reason it's worth supporting IMO is that with most packages you
can "resume" after a failld build by manually running debian/rules
build. When fixing compile errors in a large package I don't want to
have to restart the build from scratch after every file I fix.
Of course I will do a "proper" build with dpkg-buildpackage at the end
but only after i've fixed all the compile errors.