[lld] [WIP/RFC][ELF][PowerPC] Don't assume TOC pointer is valid in IPLT entries (PR #207555)

[Jessica Clarke via llvm-commits]

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jrtc27 wrote:

This test doesn't actually check the IPLT entry, which is a bit sad... something to fix regardless of what happens to this change

https://github.com/llvm/llvm-project/pull/207555