[lld/COFF] Fix -start-lib / -end-lib more after reviews.llvm.org/D116434 (#124294)

This is a follow-up to #120452 in a way.

Since lld/COFF does not yet insert all defined in an obj file before all
undefineds (ELF and MachO do this, see #67445 and things linked from
there), it's possible that:

1. We add an obj file a.obj
2. a.obj contains an undefined that's in b.obj, causing b.obj to be
added
3. b.obj contains an undefined that's in a part of a.obj that's not yet
in the symbol table, causing a recursive load of a.obj, which adds the
symbols in there twice, leading to duplicate symbol errors.

For normal archives, `ArchiveFile::addMember()` has a `seen` check to
prevent this. For start-lib lazy objects, we can just check if the
archive is still lazy at the recursive call.

This bug is similar to issue #59162.

(Eventually, we'll probably want to do what the MachO and ELF ports do.)

Includes a test that caused duplicate symbol diagnostics before this
code change.

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