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

[Matt Arsenault via cfe-commits]

================
@@ -14,6 +14,12 @@
 #include "hip/hip_version.h"
 #endif // __has_include("hip/hip_version.h")
 
+#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