[clang] [CIR][AMDGPU][NFC] Add CIRGenBuiltinAMDGPU file to support AMDGPU builtins codegen (PR #179237)

[Andy Kaylor via cfe-commits]

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@@ -1802,6 +1802,9 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   LValue emitMemberExpr(const MemberExpr *e);
 
+  /// Emit a call to an AMDGPU builtin function.
+  mlir::Value emitAMDGPUBuiltinExpr(unsigned builtinID, const CallExpr *expr);
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andykaylor wrote:

```suggestion
  std::optional<mlir::Value>
  emitAMDGPUBuiltinExpr(unsigned builtinID, const CallExpr *expr);
```

https://github.com/llvm/llvm-project/pull/179237