[lld] [ELF] Demote symbols in /DISCARD/ discarded sections to Undefined (PR #69295)

[Fangrui Song via llvm-commits]

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@@ -7,6 +7,11 @@
 
 # ERR: error: {{.*}}.o has an STT_TLS symbol but doesn't have an SHF_TLS section
 
+## As a corner case, when /DISCARD/ is present, demoteLocalSymbolsInDiscardedSections
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MaskRay wrote:

Added a TODO.

Yes, this is pretty much an edge case. We probably only want to add an error if the change does not have performance regression.

https://github.com/llvm/llvm-project/pull/69295