[ld64.lld][MachO] Add support for the -r flag

-r has not been implemented yet. This feature is useful for creating a single object file that only exposes specified symbols.

https://github.com/llvm/llvm-project/blob/main/lld/MachO/Driver.cpp#L68

Start at lld/MachO/Driver.cpp around the linked line and inspect how linker options are parsed and dispatched. Determine the work needed for -r to create a single object file while exposing only specified symbols; the feature is done when that behavior is supported by ld64.lld.

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