bundled build flags

[wangfenjin]

According to #65 , I found out that the released asset from duckdb repo is different from our bundled release, as they might use different flags. eg. windows

It will make some of the features not supported in our bundled build, for example, test_insert_duplicate succeed using the released asset, but failed in bundled version when build from source.

We may need to set the flags same to the released version of duckdb, in build.rs

[wangfenjin]

@Michael-F-Bryan If you are using bundled version, you may also need pay attention to this. It related to the ignored tests

[snth]

Do you think we could enable the setting of optional flags in build.rs through Rust feature flags by guarding some code blocks with them?

I might give that a try.