[clang] Update stdckdint.h and make it available in pre-C23 modes. (PR #69649)

[Aaron Ballman via cfe-commits]

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@@ -23,6 +23,7 @@
 
 #if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
 #define __STDC_VERSION_STDCKDINT_H__ 202311L
+#endif
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AaronBallman wrote:

GCC exposes this value in all C and C++ language modes, so we should go ahead and remove the `#if` entirely and just always define the macro.

https://github.com/llvm/llvm-project/pull/69649