Build shared libraries for lib{athdir,dsk,gms,locker,moira,usp,Xj}

[andersk]

The seven libraries we package for Debathena are currently only available as static libraries. This causes two problems. First, changing the libraries requires recompiling any binaries that use them. Second, Debian policy requires shared libraries to be compiled with -fPIC and static libraries without; that means that static libraries may not be linked into shared libraries, and indeed this causes problems on some architectures (at least amd64).