[clang] [clang][HIP] Make some math not not work with AMDGCN SPIR-V (PR #128360)

[Matt Arsenault via cfe-commits]

================
@@ -33,6 +33,13 @@
 #define __DEVICE__ static __device__ inline __attribute__((always_inline))
 #endif
 
+#pragma push_macro("__PRIVATE_AS")
+
+#ifdef __SPIRV__
+#define __PRIVATE_AS __attribute__((address_space(0)))
+#else
+#define __PRIVATE_AS __attribute__((address_space(5)))
+#endif
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arsenm wrote:

```suggestion
#define __PRIVATE_AS __attribute__((opencl_private))
```

https://github.com/llvm/llvm-project/pull/128360