[clang] [clang][NFC] move traits to tablegen (PR #201491)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,556 @@
+class Trait<string P> {
+  string Prefix = P;
+  string Spelling = "";
+  string StdName = "";
+  string KeyFlag = "KEYCXX";
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AaronBallman wrote:

It'd be nice to avoid using strings for this -- these keys are already pretty complicated and I expect we'll find more delineations to make in the future.

https://github.com/llvm/llvm-project/pull/201491