gRPC uses `upb`, but normally it vendors-in the dependency. The
vendored-in version uses a single library artifact, and the generated
pkg-config file simply adds `-lupb`. In `vcpkg` we use the `upb`
package. This has more libraries, and thus more `-lupb_*` options are
needed. Ideally we would use a `upb.pc` file, but that does not exist.
