Is this still an issue?
Also for other (newer) Ubuntu versions (e.g. 16.04 and 16.10)?
Or has it been integrated into the sources in the meantime?
I answer myself - yes, this patch (or Saint's version) is still needed and not integrated in the sources.
So I added it by myself to rockboxdev.sh (and also added some lines to ignore existing build directories instead of failing)
On a native Ubuntu 16.10 version the cross compiling works now.