[clang] [llvm] [SystemZ][z/OS] Refactor AutoConvert.h to remove large MVS guard (PR #143174)

[via llvm-commits]

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@@ -25,6 +26,16 @@
 #define CCSID_UTF_8 1208
 #define CCSID_ISO8859_1 819
 
+#ifndef STDIN_FILENO
+#define STDIN_FILENO 0
+#endif
+#ifndef STDOUT_FILENO
+#define STDOUT_FILENO 1
+#endif
+#ifndef STDERR_FILENO
+#define STDERR_FILENO 2
+#endif
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tltao wrote:

Why do we need to define these here, shouldn't they be defined in `unistd.h`? Or is that header not available on all platforms?

https://github.com/llvm/llvm-project/pull/143174