declare the libsodium dependency
declare the libsodium dependency

Summary: Folly has an optional libsodium dependency.  Declare that in folly getdeps manifest so that the relevant code is built and tested in CI.

Reviewed By: yfeldblum

Differential Revision: D34028478

fbshipit-source-id: 5e7c2f86602b94a3a975907adf8bd04f49ec33c0

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