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

[Sean Perry via cfe-commits]

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@@ -11,6 +11,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/Config/config.h"
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perry-ca wrote:

This is needed for the change in SystemZ.h to replace the hard coded `"z10"` string with the CLANG_SYSTEMZ_DEFAULT_ARCH cmake variable.  This applies to the other comment too.

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