[llvm] [LTO] Teach computeLTOCacheKey to return std::string (NFC) (PR #105331)

[Kazu Hirata via llvm-commits]

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@@ -89,9 +89,9 @@ extern cl::opt<bool> EnableMemProfContextDisambiguation;
 // Computes a unique hash for the Module considering the current list of
 // export/import and other global analysis results.
 // The hash is produced in \p Key.
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kazutakahirata wrote:

Done.

https://github.com/llvm/llvm-project/pull/105331