[clang] [clang]Implement the c23 stdc bit builtins (PR #185978)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,19 @@
+#ifndef LLVM_CLANG_TEST_STDBIT_H
+#define LLVM_CLANG_TEST_STDBIT_H
+
+#define stdc_leading_zeros(x) (__builtin_stdc_leading_zeros((x)))
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AaronBallman wrote:

CC @michaelrj-google @enh-google for more opinions on whether this looks sufficiently similar to what libc implementations will do in practice. I don't think this is accurate though because there's no external symbol to get a function pointer from; I would have expected this to be using `_Generic`.

https://github.com/llvm/llvm-project/pull/185978