(#3793) Add build dependency for std_local_ref

Some cmake targets in a UW_BUILD depend on .cpp files that get generated
with stub_gen, but the dependencies are not spelled out explicitly in the
cmake rules; which breaks larger parallel builds (eg, make -j24), when
stub_gen gets called before it is built.

This change forces correct build order on targets that depend on
{receivers,senders,switches}.cpp (which are generated by stub_gen).