Fix buck2 targets command for non-ocamlrep users of the fbcode shim (#3563)

Summary:
X-link: https://github.com/facebook/ocamlrep/pull/79
Pull Request resolved: https://github.com/pytorch/executorch/pull/3563
X-link: https://github.com/facebook/folly/pull/2185

Test Plan: CI on the ocamlrep PR passes

Reviewed By: shayne-fletcher

Differential Revision: D57006939

Pulled By: bigfootjon

fbshipit-source-id: bd70508ee634e8089b41f19cbfd471a6a7b9901d