Fix various build issues
    
    * Require libxslt and docbook-dtds for building documentation
    * Require clang and llvm for building JIT bitcode
    * Package JIT bitcode in llvmjit subpackage
    * Drop devel subpackage as upstream no longer installs liblwgeom
    * Fix various issues with shared object names and versions
    * Strip -fstack-clash-protection from compiler flags for clang