[llvm] [llvm-gsymutil] Option --symtab-file to specify a separate binary (PR #79898)

[Greg Clayton via llvm-commits]

================
@@ -92,6 +92,7 @@ static uint64_t SegmentSize;
 static bool Quiet;
 static std::vector<uint64_t> LookupAddresses;
 static bool LookupAddressesFromStdin;
+static std::string SymbolTableFilename;
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clayborg wrote:

Make optional?:
```
static std::optional<std::string> SymbolTableFilename;
```

https://github.com/llvm/llvm-project/pull/79898