build-sys: add libsystemd-id128 as libudev dependency

build-sys: add libsystemd-id128 as libudev dependency

After d848b9cbfa0 'Move generic specifier functions to shared' libudev
depends (through) libsystemd-shared.la on libsystemd-id128.so.  The
problem only appears when the linker does not support --gc-sections
and manifests itself as the inability to resolve sd_id128_get_machine
and other libsystemd-id128 functions, which aren't really used.