`dfx build` and `dfx deploy` should be able to pass additional command line arguments to `moc`

[vporton]

dfx build (and dfx deploy) should have the feature to pass an additional command line arguments to moc.

It is needed, for instance, for conditional compilation (passing different --package arguments to moc would solve my problem).

[lwshang]

This doesn't seem to be an issue with Rust CDK but rather with general development using dfx.