[lld] [lld] Use position independent argument parsing for Unresolved Symbol (PR #123950)

[Fangrui Song via llvm-commits]

MaskRay wrote:

NAK.  --allow-shlib-undefined & --unresolved-symbols are position dependent in GNU ld and our behavior follows it. Note: gold typically has larger behavior divergence, and its behavior should be taken with a grain of salt.

This patch changes the behavior to be mixed-dependent-and-independent, which is worse than purely position-dependent.

https://github.com/llvm/llvm-project/pull/123950