[lld] [ELF] Add target-specific relocation scanning for x86 (PR #178846)

[Peter Smith via llvm-commits]

smithp35 wrote:

The critical part to cause the failure seems to be the `-u,__msan_va_arg_overflow_size_tls` when we get to elf::postScanRelocations the symbol is not treated as a TLS symbol which means we early exit at https://github.com/llvm/llvm-project/blob/main/lld/ELF/Relocations.cpp#L1356 so a GOT entry is not created.

Not sure why this worked in the previous code-path, it seems like -u <symbol> should not remove the TLS flag from an existing undefined TLS <symbol> particularly as TLS relocations are only legally allowed to be resolved against TLS symbols.

https://github.com/llvm/llvm-project/pull/178846