See also: - https://github.com/protocolbuffers/protobuf/issues/10899 - https://github.com/protocolbuffers/protobuf/pull/10900 Also updates flags to deal with various compile-time warnings/errors for protobuf libs on all platforms.
This also normalizes the structure of all submodule folders so that there is a clear place to put configurations, outside the submodule source, but limited in scope to that folder. Issue #1047 (New build system)