[libc-commits] [libc] [libc] Add `returns_twice` attribute to `setjmp(3)` (PR #124370)

[Nick Desaulniers via libc-commits]

================
@@ -45,6 +45,9 @@
 #define __NOEXCEPT throw()
 #endif
 
+#undef _Returns_twice
+#define _Returns_twice [[gnu::returns_twice]]
+
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nickdesaulniers wrote:

```suggestion
```
The `[[]]` syntax is still too nascent for users; let's stick with the existing style of just providing the GNU C extension style below.

https://github.com/llvm/llvm-project/pull/124370