[clang] [z/OS] Set the default arch for z/OS to be arch10 (PR #89854)

[Fangrui Song via cfe-commits]

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@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/Config/config.h"
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MaskRay wrote:

unneeded include

https://github.com/llvm/llvm-project/pull/89854