Hello Steve, it seems we committed fixes more or less at the same time. I studied your patch but did not see the point. The makefiles in the subdirectories inherit the CFLAGS and CXXFLAGS from the top level makefile which already contains dpkg-buildflags calls. The problem on armhf seems to be a missing -fPIC which is not injected by dpkg-buildflags. I added this flag in my last upload.
Regards Christoph BTW: Did you test building on armhf?
