[lld][WebAssembly] Don't GC library objects under `--whole-archive`

Followup on https://reviews.llvm.org/D85062 which ignores
entire library objects when no symbols are used within them.
This is shouldn't apply with `--whole-archive` since this
is specified to treat them like direct object inputs.

Differential Revision: https://reviews.llvm.org/D89290