[clang] [TargetVersion] Only enable on RISC-V and AArch64 (PR #115991)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown  -fsyntax-only -verify %s
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AaronBallman wrote:

```suggestion
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -verify %s
```

https://github.com/llvm/llvm-project/pull/115991