[clang] [C23] Implement N3018: The constexpr specifier for object definitions (PR #73099)

[Mariya Podchishchaeva via cfe-commits]

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@@ -1862,6 +1862,17 @@ class StringLiteral final
     llvm_unreachable("Unsupported character width!");
   }
 
+  // Get code unit but preserve sign info.
+  int64_t getCodeUnitS(size_t I, uint64_t BitWidth) const {
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Fznamznon wrote:

FYI https://github.com/llvm/llvm-project/pull/73099#pullrequestreview-1765410034 .

https://github.com/llvm/llvm-project/pull/73099