[clang] [llvm] [SystemZ] Add i128 support for z/OS XPLINK64 ABI (PR #223026)

[Ulrich Weigand via cfe-commits]

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@@ -160,12 +162,14 @@ struct s11 {
 // CHECK-NEXT:         8 |   char b
 // CHECK-NEXT:           | [sizeof=16, align=8]
 
+#ifdef INT128_A
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uweigand wrote:

Well, this is exactly the problem you run into by making the very availability of the `__int128_t` type dependent on a feature.  I still do not think this is a good idea.   But if you do have to do that, you could just check for the feature via `#ifdef __VX__` rather than introducing another define.

https://github.com/llvm/llvm-project/pull/223026