fix(parquet): Add support for weak functions to register parquet readers and writers

[kgpai]

Summary:
This diff marks the registerParquetfactory functions with the weak attribute. The weak attribute allows the linker to discard the weaker implementation of the registerParquetfactory functions and in place use the stronger one (See: https://en.wikipedia.org/wiki/Weak_symbol).
This should remove the need to compile the same files with different options, leading to ODRs when both targets are added as dependencies to the same binary.

Differential Revision: D67301778

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D67301778

[netlify]

✅ Deploy Preview for meta-velox canceled.

Name	Link
🔨 Latest commit	ffb483a
🔍 Latest deploy log	https://app.netlify.com/sites/meta-velox/deploys/6760a7208595d80008b37e23

[kgpai]

cc: @majetideepak Some code cleanup so internally we dont have ODR violations.

[majetideepak]

@kgpai The same Wikipedia article mentions as such, inserting them into code is not very portable. Can you please share the issue you are seeing internally?

[majetideepak]

This should remove the need to compile the same files with different options When does this happen?

[kgpai]

This should remove the need to compile the same files with different options When does this happen?

This happens internally - Not sure if you recall but we had to create two targets one with VELOX_ENABLE_PARQUET defined and one without it . The one with it defined is only used for tests and the other is used everywhere else where we have the registration code. This is problematic with our internal tools like automated linters which do not use the right dependency many times causing folks to link against the PARQUET enabled target and see linking errors or at worst runtime errors.