[clang] [Clang][TableGen] Use StringRef in FlattenedSpelling (PR #113809)

[Rahul Joshi via cfe-commits]

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@@ -49,40 +49,38 @@ using namespace llvm;
 namespace {
 
 class FlattenedSpelling {
-  std::string V, N, NS;
+  StringRef V, N, NS;
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jurahul wrote:

In short, I'll defer it to you. If we don't want to commit this, I am fine and the find the reasoning behind if reasonable as well :)

https://github.com/llvm/llvm-project/pull/113809