This yields several benefits:
1. The code no longer needs to be bootstrapped (since it no longer depends on upb reflection).
2. The upb code generator no longer depends on libprotobuf at all (except for `code_generator_lite.{h,cc}`, which is just one .cc file and has no deps).
PiperOrigin-RevId: 672280579
This installs a upb's static library, headers, and three protoc plugin binaries (upb, upbdefs, upb_minitable). These will now be enabled by default, but can be disabled by setting protobuf_BUILD_LIBUPB=OFF.
To qualify this, we hook into our existing install test infrastructure which attempts to build and run our tests without any of the installation artifacts available from the source tree. Public headers are deleted, and builds of exported libraries/binaries are disabled.
PiperOrigin-RevId: 617376961
Joshua Haberman
Mike Kruskal