Case: `PROVIDE(f1 = bar);` when both `f1` and `bar` are in separate
sections that would be discarded by GC.
Due to `demoteDefined`, `shouldAddProvideSym(f1)` may initially return
false (when Defined) and then return true (been demoted to Undefined).
```
addScriptReferencedSymbolsToSymTable
shouldAddProvideSym(f1): false
// the RHS (bar) is not added to `referencedSymbols` and may be GCed
declareSymbols
shouldAddProvideSym(f1): false
markLive
demoteSymbolsAndComputeIsPreemptible
// demoted f1 to Undefined
processSymbolAssignments
addSymbol
shouldAddProvideSym(f1): true
```
The inconsistency can cause `cmd->expression()` in `addSymbol` to be
evaluated, leading to `symbol not found: bar` errors (since `bar` in the
RHS is not in `referencedSymbols` and is GCed) (#111478).
Fix this by adding a `sym->isUsedInRegularObj` condition, making
`shouldAddProvideSym(f1)` values consistent. In addition, we need a
`sym->exportDynamic` condition to keep provide-shared.s working.
Fixes: ebb326a51f
Pull Request: https://github.com/llvm/llvm-project/pull/111945
1c6688ae34