rubygem-google-protobuf: Use hidden symbols

[dan.mcgregor_usask.ca]

Summary

The Linux and Darwin builds hide the symbols in the native shared
object. This prevents some symbol collisions if this gem is loaded
alongside certain others (that should probably also hide their symbols).

This fixes numerous issues with gitaly and protobuf 3.20 and newer.

[dan.mcgregor_usask.ca]

Also created this pull request.

[mfechner]

Thanks a lot, I tested it and can confirm that fixes the problem. @sunpoet could you please commit this, as you are the maintainer of these ports.
Thanks a lot.

[dan.mcgregor_usask.ca]

Thanks for taking a look. I don't think the change to the 3.19 port is strictly necessary, but as I said in a private email to @mfechner, I do believe that hiding symbols is good practice for ruby gems.

The change to 3.2x *is* necessary, though.

[sunpoet]

Thanks!