[lld] [lld][WebAssembly] Report undefined symbols by default -shared/-pie builds (PR #75242)

[Derek Schuff via llvm-commits]

https://github.com/dschuff commented:

The biggest part of this change is the addition of the new symbol kind. Can you add to the commit message describing that (maybe it even needs to be the commit title? not sure). And can you also add a tool-conventions change to document?

https://github.com/llvm/llvm-project/pull/75242