[lld] [LTO][ELF][lld] Use unique string saver in ELF bitcode symbol parsing (PR #106670)

[Kazu Hirata via llvm-commits]

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@@ -335,6 +339,12 @@ class BitcodeFile : public InputFile {
   void postParse();
   std::unique_ptr<llvm::lto::InputFile> obj;
   std::vector<bool> keptComdats;
+
+private:
+  StringRef saved_symbol(const char *S);
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kazutakahirata wrote:

I actually take back what I said above.  When you have `std::string`, it can be implicitly cast to either `StringRef` or `const Twine &`, causing ambiguity.  The same story probably applies to `const char *`.

https://github.com/llvm/llvm-project/pull/106670