I've just seen your most recent email in passing and don't know the context, but it's extremely important: because of the license of GDB and its components, almost any package with Build-Depends: gdb-source must also set Built-Using appropriately. This is because we (Debian) have an obligation to ensure that a particular version of gdb-source remains in the archive when it's incorporated into the binary packages of some other source package. The dh_builtusing add-on is the modern way to do this. Technically Debian Policy says gdb's applicable copyright info needs to be carried over into your *binary package's* installed copyright file, but this is often overlooked and there's not an established best practice (the DEP-5 copyright file specification, for example, doesn't specify a way to do this sensibly).
I will read this thread more closely tomorrow, but wanted to say this without delay: it's a serious issue to omit Built-Using when it would be required. If you haven't done so, I'll offer my help after I get a good night's rest.
