This is a sketch of how to build and run Postgres on Bazel for Linux x64. As a sketch, it's not an end-to-end solution; you'll need to glue it together for your specific environment. For Darwin, I downloaded the prebuilt Homebrew binaries instead of building.
We compile the Postgres source into a mostly statically-linked Linux binary. Postgres is quite difficult to compile completely statically, so we bundle all necessary libs and rely on the user setting LD_LIBRARY_PATH.
We apply a small patch, allow_root.patch to disable Postgres binaries from checking for UID 0, the root user. We want to allow root users to run Postgres because we'll run postgres mostly in Docker containers. We don't want to have to create a postgres user just to appease Postgres.
To invoke the Postgres binaries, you must set the LD_LIBRARY_PATH so Postgres will link against the bundled version of glibc.