Tempo's third party dependencies
Scripts/build_grpc_<platform>.sh builds gRPC, Protobuf and Abseil as static libraries against the
Unreal Engine's OpenSSL and zlib (UNREAL_ENGINE_PATH must point at the engine), then links them
whole into one shared library, tempogrpc (Utils/tempogrpc). Tempo's modules all share that one
copy of the libraries, which keeps their global state (Protobuf's descriptor pool, gRPC's core) from
being duplicated across modules. Patches/gRPC.patch builds the grpc++ libraries with default
visibility so the shared library can export gRPC's C++ API, which is not annotated for export.
The Linux build is a cross-compile from Windows, run after the Windows build.