can support greenplum6？

[wonb168]

No description provided.

[JelteF]

Are there any specific issues you hit when compiling for Greenplum? If so, feel free to list them here and/or create a PR for those.

[wuputah]

Closing in favor of consolidating in #154... though I'll say I personally think Greenplum is a bit less likely since the source code seems to have gone closed source, so it's hard for us to test and officially support. Regardless, would be happy to see a PR to fix any issues.