[clang] [clang][Basic] Add helper APIs to get language version codes from LangOptions (PR #163348)

[via cfe-commits]

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@@ -184,6 +184,28 @@ class LangOptionsBase {
     HLSL_202y = 2029,
   };
 
+  /// C language version codes as defined by the standard.
+  enum CLangStd : uint32_t {
+    // FIXME: Use correct value for C2y.
+    C_2y = 202400,
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yronglin wrote:

Agree, `C2y` seems more make sense.

https://github.com/llvm/llvm-project/pull/163348