[llvm] [Offload] add 'olIterateSymbols' runtime function (PR #213036)

[via llvm-commits]

blazej-smorawski wrote:

Seems that the symbol has no `SymbolRef::SF_Global` flag which is 2. I will investigate further.
```
call *FlagsOrErr
(std::remove_reference_t) $19 = 0
call Symbol.getName()
(llvm::Expected<llvm::StringRef>) $20 = {
   = {
    TStorage = (Data = "read", Length = 4)
    ErrorStorage = llvm::ErrorInfoBase @ 0x0000555555e67e0c {
      pointer = 0x0000555555e67e0c
    }
  }
  HasError = false
  Unchecked = true
}
```

https://github.com/llvm/llvm-project/pull/213036